Lookout Slough, a vast 3,400-acre wetland situated on the periphery of the Sacramento-San Joaquin Delta in central California, now teems with aquatic life, its waters rhythmically pulsing with tides flowing from the distant San Francisco Bay. This vibrant ecosystem, home to a diverse array of fish, amphibians, reptiles, and birds, represents a dramatic transformation from its recent past. Just two years ago, this land was dry former farmland, isolated from the Sacramento River’s natural floodplain by a formidable 26-foot-tall levee. This ambitious undertaking, recognized as the largest tidal restoration project in the Delta, was directly prompted by the alarming decline of the Delta smelt, a diminutive fish scarcely longer than an index finger.

The Delta smelt, uniquely adapted over millennia to the Delta’s brackish tidal environment, serves as a crucial indicator of the region’s ecological health. Its dwindling numbers signal a critical deficit in the essential phytoplankton and zooplankton that form the base of the food web, consequently impacting the availability of sustenance for birds and larger fish. Charlotte Biggs, program manager for the California Department of Water Resources (DWR), aptly likened the smelt’s significance to a vital blood test, offering insights into the broader well-being of the Delta’s complex biological systems. The central question now facing scientists and conservationists is whether the extensive restoration efforts, exemplified by projects like Lookout Slough, can indeed revitalize this imperiled species.

Historically, the Sacramento-San Joaquin Delta has been one of California’s most ecologically rich and agriculturally productive regions, a natural confluence where the saltwater of San Francisco Bay mingles with the freshwater flowing from the Sacramento and San Joaquin rivers. For thousands of years prior to European settlement, Indigenous peoples, including the Miwok, Maidu, and Yokut communities, thrived along its fertile riverbanks and intricate network of waterways, relying on its bounty for sustenance and cultural practices.

The 20th century, however, ushered in a new era of water management driven by the state and federal governments’ vision for California’s burgeoning cities and expansive agricultural industry. To control flooding and facilitate the development of vast orchards and tomato fields, extensive networks of levees were constructed throughout the Delta, effectively taming its natural waterways. By 1969, the establishment of seven massive impeller pumps belonging to the California State Water Project marked a pivotal moment, initiating the diversion of significant volumes of freshwater. These powerful pumps moved water over a 244-foot hill near Tracy, channeling it through an intricate system of aqueducts to irrigate farmlands in the Central Valley and supply the growing demand of cities further south.

This large-scale water diversion had profound and detrimental consequences for the Delta smelt. The pumping operations effectively dried up the fish’s vital spawning grounds, diminished the crucial tidal flows that delivered essential microorganisms, and eliminated the protective aquatic vegetation that shielded young smelt from predators. In the early 2000s, this ecological disruption led to a catastrophic collapse in the Delta smelt population, mirroring the precipitous declines observed in other key Delta species, including the longfin smelt, striped bass, and threadfin shad.

In 2008, nearly four decades after the Tracy pumps began their relentless diversion, the U.S. Fish and Wildlife Service recognized the severity of the impact. A federal ruling determined that the extensive freshwater diversion posed a significant threat to critical fish habitat, mandating the restoration of approximately 8,000 acres of wetland and stream ecosystems. This pivotal decision initiated California’s long-term commitment to rectifying the ecological damage caused by its own water management practices.

Over the subsequent decade, the DWR identified and commenced work on ten separate restoration sites within the Delta, encompassing a total of roughly 5,000 acres. Each of these projects involved the challenging task of dismantling one or more of the historical levees that had severed the land from its vital connection to the water. However, with an additional 3,000 acres still requiring restoration to meet the federal mandate, the state acknowledged its limitations and the necessity of engaging external expertise. This realization paved the way for the involvement of what are often termed "biodiversity brokers."

Under the framework of federal and numerous state laws, private and public developers are legally obligated to compensate for the environmental impacts of their projects on designated waterways and vulnerable species. This mitigation requirement typically involves funding the restoration of comparable habitat elsewhere. Many entities fulfill this obligation by purchasing mitigation credits from specialized private companies that focus on ecological restoration. This practice, known as mitigation banking, emerged in the 1980s and has experienced remarkable growth over the past two decades, evolving into a multi-billion-dollar industry.

In 2018, the state of California issued a formal request for proposals to undertake the restoration of the remaining 3,000 acres of riparian habitat. Adam Davis, co-founder and managing director of Ecosystem Investment Partners (EIP), a prominent firm in the mitigation banking sector, responded to this call. His company acquired the 3,400 acres that now constitute Lookout Slough with the explicit objective of restoring the site and subsequently generating mitigation credits for sale.

EIP finalized an agreement with the state in 2018 and commenced groundbreaking activities at the Lookout Slough site in June 2022. Approximately a year later, during a visit with Davis, the transformation was palpable. Standing atop the levee that once encircled the slough, the sounds of bulldozers, scrapers, and dump trucks filled the air as they worked on the property destined for inundation. "People forget," Davis remarked, "that underneath all the ecology – the fish, the migration corridors, the places where birds need to land – underneath all that is land that people own." He articulated how mitigation banking strategically leverages private land ownership for conservation purposes, creating essential financial incentives to curb the accelerating rates of species extinction and land degradation.

To prepare the land to receive the restored tidal flows, EIP and its contracting partners meticulously engineered the landscape, excavating intricate networks of channels and indentations. These features were designed to slow down river and tidal currents, thereby creating optimal spawning and nursery habitats for fish and amphibians. Over a two-year period, approximately 26 miles of channels were carved across the 3,400 acres of Lookout Slough, involving the relocation of an estimated 30,000 dump truck loads of soil. As a result of this extensive restoration work, EIP was awarded 2,975 mitigation credits, for which the state paid a substantial sum of $32,605 per credit, totaling nearly $97 million.

In September 2024, a return visit coincided with the dramatic breaching of the levees. As a bulldozer systematically dismantled sections of the earthen barrier, water surged across the landscape, heralding the return of tidal influence. Eighteen months later, the site had evolved into a complex mosaic of water channels and partially submerged islands. Teenagers were observed fishing from the banks, pelicans soared overhead, and a flock of geese paddled serenely near distant, low-lying islands, indicating the early stages of ecological resurgence. However, as of this report, the DWR has not yet documented the presence of Delta smelt within the slough.

The restoration of Lookout Slough and other Delta landscapes, while critically important, may have arrived too late for the Delta smelt itself. The species’ population has plummeted by an astonishing 99% since it was first listed as federally threatened by the Fish and Wildlife Service in 1993. Despite repeated efforts involving the release of hatchery-raised smelt in recent years, weekly surveys conducted by the Fish and Wildlife Service consistently report population numbers in the single digits, underscoring the species’ precarious status.

"The smelt used to be among the most common fish species in the Delta," stated Jon Rosenfield, a fish biologist and science director for San Francisco Baykeeper, an environmental advocacy organization. "Now, it’s almost impossible to find them." Rosenfield acknowledged the admirable nature of the restoration efforts but expressed concern about their adequacy, metaphorically describing the situation as "like building a very nice playground in a neighborhood you’ve allowed to burn down."

Despite these sobering assessments, Dan Riordan, section manager for tidal habitat restoration at DWR, offered a more optimistic perspective. He reported that the state has documented the presence of phytoplankton and zooplankton within the slough, key indicators of developing smelt habitat. These findings are slated for inclusion in a comprehensive report scheduled for release in September.

More than five decades after the powerful pumps in Tracy began siphoning the Delta’s vital freshwater, the plight of the Delta smelt has compelled a significant return of water to the land. If these restored wetlands continue their recovery trajectory, they hold the potential to provide enduring and essential habitat for a multitude of species. Whether the Delta smelt will ultimately be among the beneficiaries of these extensive ecological interventions remains to be seen, but the ongoing restoration efforts represent a critical step towards a more balanced and resilient Delta ecosystem.