California Is Turning 15,000 Acres of Salt Ponds Back Into Tidal Marsh — What’s Flying In Is Unreal.

In February of 2026, a biologist named Rachel Turties stood on a levee in Mountain View, California, and watched a bulldozer cut through a wall of compacted earth that had held back the San Francisco Bay for more than a century. Within minutes, saltwater surged through the gap and flooded a 435-acre pond that had not tasted tidewater since before the first automobile rolled off a factory line. The pond had spent its entire modern existence evaporating seawater into industrial salt. Now it was being handed back. Turtis, a wildlife biologist with the United States Fish and Wildlife Service, described what would come next. She said that visitors would be able to watch the pond gradually transform into a verdant and vibrant marshland. She was not guessing. She had seen it happen before, at other ponds in the same project. And what had shown up at those sites was not what anyone had predicted. Endangered birds that had not been seen in the South Bay in decades materialized in restored marshes within years. Overwintering waterbird populations doubled, fish returned to channels that had been barren for generations. And all of it happened faster than any model had forecast. This is the story of how California is turning 15,000 acres of industrial salt ponds back into tidal wetlands, and how the birds and animals flying, swimming and crawling back into those wetlands are rewriting what scientists thought they knew about ecological recovery. To understand why this matters, you need to know what was here before. About 3,000 years ago, as sea level rise along the Pacific coast began to slow, Marsh plants took hold along the edges of San Francisco Bay. Cordgrass colonized the lowest tidal flats, the places that flooded twice a day with every tide cycle. Pickleweed crept in behind it, filling the slightly higher ground where saltwater reached only during the highest tides of the month. Over centuries, these plants trapped sediment carried in by rivers and tides, building the ground upward, inch by inch, until it rose above the daily reach of saltwater. The result was one of the most productive ecosystems on the planet. At its peak, roughly 190,000 acres of tidal marsh surrounded the bay. 6,000 miles of tidal channels threaded through the vegetation like capillaries through living tissue. These marshes did things that no human infrastructure could replicate at any price. They filtered pollutants from runoff water before it reached the bay, They absorbed storm surges that would otherwise flood low-lying towns. They sequestered carbon in their deep peat soils. They served as nurseries for salmon, steelhead, herring, and dozens of other fish species that depended on the sheltered, nutrient-rich shallows for spawning and rearing their young. And they provided critical habitat for millions of migratory birds traveling the Pacific Flyway, a corridor stretching more than 4,000 miles from the Arctic tundra of Alaska and Canada To the wetlands of Mexico and Central America, San Francisco Bay sat at the geographic center of that flyway. It was the largest estuary on the entire Pacific coast of both North and South America. Birds that had flown thousands of miles without stopping needed it the way a long-distance runner needs a water station. Shorebirds refueled on its mudflats, gorging on tiny invertebrates buried in the sediment. Waterfowl wintered in its shallows by the hundreds of thousands. Herons, egrets and terns hunted its channels. In a single spring migration in the 1980s, researchers counted more than 200,000 birds gathered in the salt ponds along the South Bay. The Bay was not just a stop on the flyway. For many species, it was the stop, the one place where the food supply was rich enough, the habitat varied enough, and the water shallow enough to sustain the enormous enormous caloric demands of transcontinental flight. But by the time those counts were taken, the marsh was almost gone. The destruction began in 1853, when a German settler named John Johnson built the first artificial salt ponds along the South Bay shoreline. The process was simple. You diked off a section of marsh, let seawater flood in, and waited for the California sun to evaporate the water, leaving crystallized salt behind. Small family operations proliferated along the shore. In 1868, California removed all limits on the amount of marshland a single entity could acquire, and what had been a handful of modest operations exploded into an industrial enterprise. Speculators bought up thousands of acres of marsh at pennies per acre. Levees were built across entire watersheds. Creeks were rerouted or buried. The Ohlone people, who had lived along these shores for thousands of years and had harvested salt by traditional methods, watched their ancestral landscape disappear beneath an industrial grid of straight-edged evaporation ponds. By the 1950s, a single company called Leslie Salt controlled roughly 25,000 acres of artificial evaporation ponds across the South Bay. Those ponds had consumed more than half of the historical tidal marshes in that part of the bay. But the salt ponds were only part of the destruction. Developers filled in even more wetland to build entire communities. Foster City, Redwood Shores, subdivisions, shopping centers, and office parks poured onto what had once been living mudflat. Highways were laid across former marshes. Airports were built on fill. The numbers are staggering. By the late 20th century, between 85 and 90% of San Francisco Bay's original tidal wetlands had been destroyed. Of the roughly 190,000 acres that once ringed the bay, only a fraction survived. 6,000 miles of natural tidal channels had been reduced to about About 1,000. Groundwater pumping had caused parts of the Santa Clara Valley to sink as much as 13 feet below sea level. The city of Alviso, sitting at the southern tip of the bay, dropped to 12 feet below the water line. What had been one of the most biologically productive estuaries on Earth had become an ecological disaster zone, ringed by levees that held back a rising bay from communities that now sat below it. And almost nobody thought it could be fixed. Here is the key insight that changed everything In the late 1990s, a group of scientists, conservationists, and government officials began asking a question that sounded almost absurd at the time. What if you could buy the salt ponds back? Not just a few of them. All of them. The company that now owned them was Cargill, which had acquired Leslie Salt's holdings, and at its peak was producing roughly a million tons of salt per year from its South Bay operations. These were not small ponds. They were visible from space. If you have ever flown into San Francisco International Airport and looked down at the strange patchwork of bright orange, pink and green pools below you, you were looking at Cargill's salt crystallizers. The colors come from different species of microorganisms and algae that thrive at different salinities, and from the mineral deposits left behind as water evaporates. The idea of buying 15,000 acres from one of the largest privately held companies in the world and giving them back to the tide was considered, by most reasonable assessments, politically impossible. The land was worth hundreds of millions of dollars, Cargill was not in the business of giving things away. Local governments relied on the salt operations for jobs and tax revenue. Environmental review alone would take years. And even if the land could be acquired, nobody knew whether marshes could actually grow back on soil that had been saturated with industrial-grade brine for over a century. The scientific consensus was cautious at best. Some ecologists argued that the chemical composition of the pond beds had been so fundamentally altered that natural revegetation was unlikely without massive, expensive soil remediation. The environmental movement in the Bay Area had been building toward this moment for decades. In 1961, a group of activists formed the Save San Francisco Bay Association in response to a proposal that would have filled in large portions of the Bay for development. Their advocacy led to the creation of the Bay Conservation and Development Commission, which restricted new fill projects. In 1974, the Don Edwards San Francisco Bay National Wildlife Refuge was established on former Leslie Salt Land, protecting some of the remaining wetland habitat. But protection was not restoration. The salt ponds remained salt ponds. The lost marsh remained lost. The person who made the acquisition happen was United States Senator Dianne Feinstein. In 2003, Feinstein brokered a deal that most people thought could not be done. The state and federal governments purchased 15,100 acres of salt ponds from Cargill for a total of $100 million. The money came from the California Wildlife Conservation Board, which contributed $72 million. The United States Fish and Wildlife Service, which added 8 million, and a consortium of private foundations, including the Hewlett, Packard and Moore Foundations, and the Goldman Fund, which contributed the remaining 20 million. It was, at the time, one of the largest wetland acquisitions in American history, and it launched what would become the biggest tidal wetland restoration project on the West Coast. The South Bay Salt Pond Restoration Project is managed by a team of agencies That includes the California State Coastal Conservancy, the United States Fish and Wildlife Service, the California Department of Fish and Wildlife, the Santa Clara Valley Water District, and the United States Army Corps of Engineers. The project spans three sites, Eden Landing near Haywood and Union City, Alviso in Santa Clara County, and Ravenswood near Menlo Park. Two of the three sites sit within the Don Edwards San Francisco Bay National Wildlife Refuge, which itself covers 30,000 acres. The plan is ambitious. Over a 50-year timeline, with a target completion somewhere around 2050, the project aims to restore as much as 90% of the 15,000 acres to tidal marsh and other wetland habitats. A 140-page adaptive management plan guides every phase of the work, prescribing monitoring protocols, decision thresholds, and contingency measures for everything from mercury contamination to invasive species. The actual work of restoration sounds deceptively simple. You breach the levees and let the bay back in. But the reality is far more complex. Dave Holsing, the executive project manager for the restoration, described it bluntly. He said that it is hard doing work in an urban environment. The project sits inside a metropolitan area that is home to roughly 8 million people. Every breach has to be engineered to manage flood risk for nearby communities. Every construction phase requires environmental review under both the California Environmental Quality Act and the National Environmental Policy Act. Levees cannot simply be demolished. They have to be reshaped into gradual transition slopes called ecotones, which allow marsh plants to migrate inland as sea levels rise, and the soil itself fights back. When the first ponds were opened around 2006, scientists faced two problems nobody had fully anticipated. The first was gypsum. Decades of salt production had left layers of gypsum crust up to 18 inches thick on the pond floors. The assumption was that nothing would grow through it. Donna Ball, the lead scientist on the project, and a biologist with the San Francisco Estuary Institute, monitored the early sites closely. She waded through the ponds in rubber boots, collecting sediment samples from ground that crunched underfoot like dried plaster. What she found surprised everyone. Marsh plants pushed through 12 inches of gypsum. The plants did not care about the crust. They found the sediment beneath it and anchored in. Ball said later that the wetlands were recovering faster than her team had predicted. She said, in her own words, that they had thought it would take longer. The second problem was mercury. Legacy contamination from Gold Rush-era mining operations had left significant mercury deposits in the sediments around Alviso. Nineteenth-century miners used mercury to extract gold from ore. And the runoff had been washing downstream into the bay for over 150 years. The concern was that breaching the levees would re-mobilize that mercury, sending it into the food chain, and poisoning the very wildlife the project was trying to protect. What actually happened was more nuanced. Mercury levels did spike briefly when tidal flow was first restored, but they dissipated faster than models predicted. New sediment carried in by the tides began to bury the contaminated layers, effectively sequestering the mercury beneath clean material. The system was cleaning itself. Not the way an engineer would clean it, with dredges and chemical treatment and hazardous waste disposal. The way nature cleans things. Layer by layer. Tide by tide. The construction itself is a massive physical undertaking. When the Mountain View Pond A2W was breached in February of 2026, the project moved 180,000 cubic yards of dirt, that is roughly 18,000 dump truck loads. Workers built five bird nesting islands designed to give ground nesting shorebirds safe platforms above the reach of high tides and predators. They constructed a half-mile habitat slope linking marsh to uplands, creating a gradual elevation transition that allows animals to move between habitats. They installed a 1.2-mile public access trail with benches, interpretive signs, and a scenic wildlife viewing area. That single pond cost $20 million to restore, funded by a combination of state water resources money, federal environmental protection agency grants, contributions from the San Francisco Bay Restoration Authority, the National Oceanic and Atmospheric Administration, and local partnerships including the City of Mountain View and Pacific Gas and Electric Company. Across the full project, the milestones have been building steadily. In 2011, A 630-acre breach opened new ponds at Alviso to tidal flow. In December of 2023, a 300-acre section of the Ravenswood R4 pond was breached in a $13 million construction effort. That event was delayed a full 12 months because a January 2023 atmospheric river storm overwhelmed the construction site. Amy Hutzel, the executive officer of the California State Coastal Conservancy, called the Ravenswood breach a milestone in what she described as the most ambitious wetland restoration project on the west coast. By early 2026, more than 3,700 acres had been opened to the bay. That is more than 25% of the total 15,000-acre project area. And an additional 700 acres of managed ponds had been enhanced for wildlife habitat, with constructed nesting islands and careful salinity management. Here is where the data broke every model. Scientists expected recovery to be slow. Tidal marshes, after all, build themselves one millimeter of sediment at a time. The conservative projections suggested it might take decades before the restored areas showed meaningful ecological activity. The models were not just wrong. They were wrong by an order of magnitude. A United States Geological Survey study tracking the project area from 2002 to 2014 found that overwintering waterbird populations in the restored ponds had more than doubled. The count went from roughly 100,000 birds to 200,000. Nearby Cargill-owned ponds that had not been restored showed virtually no change during the same period. That is not a coincidence. That is causation. The birds knew what the models did not. The habitat was ready. In 2014, just eight years after the first ponds were breached, biologists discovered Ridgeway's rails in the restored Alviso Marsh. The Ridgway's rail is a rust-colored, secretive shorebird that is federally listed as endangered. It lives only in San Francisco Bay tidal marshes. Its population had been devastated by a century of habitat loss, and a United States Geological Survey genetics study found that the surviving population carries the scars of that bottleneck in its DNA. Many scientists doubted the species would colonize newly created marsh within a single human generation. It showed up in eight years. And it was not just visiting. It was breeding. Raising chicks in pickleweed that had not existed a decade earlier. One year later, in 2015, researchers found endangered saltmarsh harvest mice, living in dense stands of pickleweed, at the same Alviso site. The saltmarsh harvest mouse is found nowhere else on Earth. It is endemic to the San Francisco Bay estuary, a tiny brown rodent about the size of a human thumb, and its survival depends entirely on the existence of healthy tidal marsh with pickleweed thick enough to hide in. Nobody connected its reappearance to the restoration at first. Then the surveys confirmed it. The mice were not just passing through, they had established a breeding population in marsh that had not existed a decade earlier, Donna Ball put the significance plainly. She said it was great to know they were having a positive effect. That is an understatement. By 2023, monitoring surveys across the project had documented more than 80 species of birds, 22 species of fish, and 10 species of invertebrates using the restored and enhanced habitats. American avocets gathered in flocks so dense they looked from the air like thousands of pearl-like brown and white dots scattered across the shallows. Northern shovelers and canvas backs. Ducks that had historically wintered in the Central Valley shifted to the South Bay ponds and thrived. Longfin smelt, a threatened fish species, appeared in surrounding waters in greater numbers than before the restoration began. Western snowy plovers, a federally threatened shorebird that nests on bare salt flats and dried pond beds, recorded their highest breeding population ever in the project area in 2023. Biologists with the San Francisco Bay Bird Including researchers Maddy Schwartz, Katie LaBarbera, and Josh Scullin, counted 368 adults during the breeding window survey. That was the highest number ever recorded in their monitoring region. They tracked 304 nests. 64% hatched successfully. At least 64 chicks fledged. The team had spread crushed oyster shells across dried ponds to give the plovers better nesting substrate And removed tall perches where raptors could sit and scan for prey. The plovers responded. Let me put that in context. These are birds that lay their speckled eggs directly on the ground. On barren salt flats. In an area surrounded by 8 million people. Red foxes. California gulls. Northern harriers. And feral cats. The fact that they are not only surviving but posting record breeding numbers in habitat that was an industrial salt factory 20 years ago is not a minor footnote. It is a fundamental challenge to the assumption that ecological recovery requires centuries. The cascade effect is what makes this story extraordinary. It is not just that birds came back. It is that each recovery triggered the next in a chain reaction that no model had anticipated. When the levees were breached, tidal flow returned. Sediment began accumulating. Marsh plants colonized the new substrate. The plants stabilized the sediment, which allowed more plants to grow. The growing marsh created shelter for small fish and invertebrates. The fish and invertebrates attracted shorebirds and wading birds. Herons and egrets stalked the new channels. Sandpipers and willets worked the mudflats. The birds deposited nutrients that fertilized the marsh. The marsh expanded, which filtered more water, which improved water quality in the surrounding bay, which supported more marine life. Every link in the chain reinforced the next. The system was rebuilding itself. Not the way engineers rebuild things. The way nature rebuilds things. Slowly, then suddenly. Dave Holsing described a shift that captures the scale of what happened. He said that the stopover has become the bay. What he meant is that migratory birds on the Pacific Flyway, which historically used the Central Valley's marshes as their primary refueling station, have shifted to the South Bay because the Central Valley's wetlands were developed out of existence. The salt ponds, even in their degraded state, had accidentally provided some of the last remaining open water habitat on the flyway. Now that those ponds are being converted to functional marsh, the birds are not just stopping over, they are staying. The bay has become the destination. Here is a detail that rarely makes it into the conversation. This is not romantic nature worship. This is hard-nosed economics. A study led by Ray Taylor Burns, a postdoctoral fellow at the University of California Santa Cruz's Center for Coastal Climate Resilience, calculated the flood reduction value of restored tidal marshes in San Mateo County alone. At current sea levels, the marshes provide about $21 million in flood reduction benefits Under 1.6 feet of sea level rise, that figure exceeds $100 million. Under 3.3 feet of rise, it reaches roughly $500 million. A narrow strip of restored marsh near San Francisco International Airport was valued at $900,000 per hectare. These are not theoretical numbers. They were calculated using the same hydrodynamic models that engineers use to design levees and seawalls. The marshes were evaluated on the exact same basis as concrete infrastructure, and they performed. The study also found that nearly half the people benefiting from these restored marshes currently live in socially vulnerable census areas, communities that would be least able to absorb the cost of flooding. A conventional seawall engineered to protect the same stretch of coastline would cost tens of millions of dollars to build, requires ongoing maintenance, electricity for pump stations, and periodic replacement as it degrades. A restored marsh costs a fraction of that to establish and then maintains itself. It grows. It adapts. It improves water quality as a side effect of existing. When sea levels rise, a healthy marsh migrates inland, building new habitat as old habitat floods. A seawall does not migrate. It sits there until the water overtops it, and then it fails catastrophically. But this is where the story gets complicated, and this is where honesty matters more than celebration. Cargill still operates salt production facilities on roughly half of its original South Bay acreage. The company produces nearly the same volume of salt it did before the land transfer, using fewer ponds more efficiently. That means workers, supply chains, and communities that depend on salt production are still tied to the ponds that have not yet been restored. The long-term plan calls for converting the vast majority of the remaining acreage to marsh. But nobody has fully addressed what happens to those jobs when the last evaporator ponds close. In 2023, Cargill salt workers in Newark went on strike. A reminder that the people who work these ponds are not abstractions in an environmental impact report. They are individuals with families, mortgages, and skills built over decades of physical labor in a demanding outdoor industry. The restoration project has created some new employment in construction, monitoring, and trail maintenance. But those jobs are temporary and specialized. They do not automatically replace the steady, year-round work of salt production. And the communities closest to the ponds, places like Alviso and East Palo Alto, are often the same communities that face the greatest flood risk and have the fewest resources to manage economic transition. There is also the biological tension that complicates the narrative. Not every species benefits equally from restoration. The western snowy plover, for instance, nests on the bare, dry salt flats that the project is converting to tidal marsh. Phase 1 of the restoration reduced available breeding habitat for plovers by roughly 19%. The December 2023 Ravenswood breach removed another 8%. The project is building artificial nesting islands and managing remaining ponds to compensate. But the tension is real. Restoring one habitat sometimes means reducing another, and the species that adapted to the artificial landscape over 150 years do not give it up willingly. There is also the question of time and money. The project has restored roughly 25% of the target area over its first two decades. The implementation cost is estimated to run from the low hundreds of millions to the high hundreds of millions of dollars, spread across many decades, and dependent on continued political support at the local, state, and federal level. In 2022, Congress passed the San Francisco Bay Restoration Act, and California voters approved a tax measure that added $8 million in annual funding over 20 years. But a single change in administration, a single budget crisis, a single reprioritization could slow or halt the work. And then there is the clock. A 2019 study by Point Blue Conservation Science found that tidal flow must be restored to certain areas by mid-century, or those areas may never accumulate enough sediment to survive rising seas. The National Oceanic and Atmospheric Administration projects that West Coast sea levels will rise 4 to 8 inches by 2050, with major floods becoming five times more frequent. The marshes need time to build themselves up. If they do not get that time, If restoration is delayed by funding gaps or political gridlock, some of those 15,000 acres may be lost permanently, not to salt production, to the ocean itself. Meanwhile, biologists are fighting a parallel battle against invasive spartina grass, a non-native species that crossbreeds with native cordgrass and threatens to overwhelm the recovering marsh. Chris Barr, the deputy complex manager of the San Francisco Bay National Wildlife Refuge complex, has spoken openly about these tensions. He emphasized that what makes this project special is that it was community-grown and community-based. The restoration was not imposed from above. It was negotiated among dozens of stakeholders over years, but community-based does not mean painless. It means that every decision carries a human cost, and that the people most affected by the transition deserve to be at the table when those decisions are made. Stand on the levee at Alviso today, and look out across the restored marsh. The ground that was a white crust of industrial gypsum, is now a dense carpet of pickleweed and cordgrass, stretching to the edge of the bay, in an unbroken sweep of green. The channels that were bone-dry trenches are now tidal waterways, where long fins smelt, and juvenile steelheads swim through water so clear you can see the bottom. The air that once carried nothing but the mineral smell of brine now fills with the calls of avocets, stilts, long-billed curlews, and marsh wrens. At Eden Landing, goldfinches and yellowthroats dart through the vegetation. Herons stand motionless in the shallows, waiting. In the tall pickleweed at Alviso, if you are patient and quiet, you might hear the secretive clatter of a Ridgway's rail. A bird that nearly vanished from this bay entirely, Calling from marsh that did not exist when the first smartphone was sold. Matt Brown, the manager of the San Francisco Bay National Wildlife Refuge Complex, said it simply. He said, they are healing San Francisco Bay, righting some of humanity's wrongs. That is not hyperbole. It is a measured statement from a federal wildlife manager who oversees seven refuges and who has watched dead ponds come back to life under his watch. What this project reveals is something that scientists have been slow to accept, and that policymakers have been even slower to fund. Natural systems, when given the chance, can rebuild faster than anyone predicts. They can outperform engineered solutions at a fraction of the cost. And they get better over time instead of degrading. A seawall erodes. A marsh grows. A pump station breaks down. A wetland adapts. A concrete channel requires electricity. A tidal creek requires nothing but gravity and the moon. The 15,000 acres of salt ponds being handed back to the bay are not just a restoration project, they are a test of whether we are willing to trust the system that built all of this in the first place. The same system that filtered the water, protected the shoreline, and fed the birds for 3,000 years before we decided we knew better. I want to know what surprised you the most. Was it the speed of the recovery? The economic value of the marsh? The fact that Think that endangered species showed up before anyone thought they would? Or was it the scale of what was lost in the first place? Tell me in the comments. If you are not subscribed yet, now is the time. We cover stories about restoration, and the people who are fixing what is broken. Hit subscribe. See you in the next one.