How Managed Wetlands are Boosting Food Production in Suisun Marsh

Suisun Marsh is a rich and vibrant environment, teeming with growth and wildlife. DWR is harnessing that natural productivity to explore a new approach to ecosystem improvement - one that works with the marsh's ability to produce the food and habitat native species need to thrive.

This approach involves strategically managing wetlands to produce and export tiny, shrimp-like organisms called zooplankton that super-charge the food web to the benefit of native fish species. It involves adjusting water levels, tracking food web production and modeling how that food moves through Suisun Marsh.

"Normally these sites are dry in the summer, which means production is zero," said Rosemary Hartman, DWR environmental program manager. "Now that these sites are wet, there are zooplankton out there, and they are at way higher densities than you get in the surrounding sloughs."

Importantly, this effort isn't driven by the needs of any single species. Its value is cumulative, with benefits that extend across the ecosystem - from improving ecological conditions to deepening the collective understanding of how the Delta functions and how it can be best managed for the future.

Putting summer tides to work

Most wetlands in Suisun Marsh are flooded in winter, providing refuge and food for migrating waterfowl. The process produces plentiful zooplankton that ducks don't eat but are a staple of the fish diet. A similar process once happened naturally in summer with the tides until the Delta was developed for agriculture. Now DWR is experimenting with what happens when water is brought back to the area.

"We want to flood these wetlands in the summer and let nature take its course," Hartman said.

It mirrors the Nigiri Project, which benefits juvenile salmon by steering them onto the Yolo Bypass floodplain, where they feast on a bountiful food supply before their journey to the Pacific Ocean.

"I think the biggest difference is that we don't expect the fish to be on the wetlands, just benefit from food exported from the wetlands," Hartman said.

How It Works

Flooding shallow, warm-water habitat mimics a natural floodplain, where decomposing plants and fast-growing algae form the base of a rapidly expanding food web. Once zooplankton reaches high density, water is released through devices called flap gates into nearby waterways where Delta smelt can feed. Hartman calls the method "salting the soup," a relatively small addition that could significantly improve the surrounding ecosystem for the tiny fish that is nearly extinct in the wild.

The work reflects a broader shift in ecosystem management for Delta smelt, using tools beyond adjusted outflow patterns. In 2025, an amendment to DWR's operating permit for the State Water Project replaced a fall outflow requirement, known as "X2," with an approach focused on improving Delta smelt food production and habitat. The California Department of Fish and Wildlife (CDFW) requires DWR to target production of as much as 13,000 pounds of zooplankton each year for the next three years. Managed wetlands are being investigated as a potential way to produce zooplankton at that scale.

Researchers are evaluating potential trade-offs. Predator surveys use hook-and-line sampling to compare the abundance of predatory fish, primarily striped bass, near wetland outlets with nearby control sites. The surveys help determine whether managed wetlands can increase food for Delta smelt without also attracting concentrations of predators.

That question is part of a larger investigation examining water quality, dissolved oxygen, waterfowl food production, mosquito management, and the movement of carbon and nutrients through the food web.

Once the data are collected, researchers from multiple agencies and universities will evaluate whether the ecological benefits outweigh potential costs. Their findings will help guide future management decisions and determine whether the program expands to other sites.

The project depends on a partnership with private duck clubs and landowners, who receive financial incentives to participate. Because summer flooding affects waterfowl management, future years may rotate participating wetlands to balance the needs of wildlife and landowners.

"This is a huge collaborative effort," Hartman said. "We're bringing together agencies, universities and partners to answer a simple but important question: Can managed wetlands produce food for fish without sacrificing habitat for waterfowl and, if not, how can we change management to balance waterfowl and fish food in Suisun Marsh?"

To see DWR scientists collecting water quality samples for the fish food project, visit the photo gallery on DWR's Pixel photo library.