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Elkhorn Slough National Estuarine Research Reserve

National Estuarine Research Reserve System

Diving Deeper Podcast: Estuaries

Preserving the 'Life Mud' of a California Estuary

American Recovery and Reinvestment Act helps NOAA improve habitat and create jobs

Parsons Slough and railroad tracks

A new sill at the Elkhorn Slough National Estuarine Research Reserve (located just north of the railroad bridge shown in the foreground) is intended to reduce the erosion of mud from the estuary. Only the sides of the sill are above water.

At the Elkhorn Slough National Estuarine Research Reserve (NERR), a 1,700-acre tidal salt marsh inland of Monterey, California, kismet recently came calling in the form of a $4.5 million grant from NOAA through the American Recovery and Reinvestment Act. The grant made possible the recent construction of an experimental underwater retaining wall, called a “sill,” that’s designed to slow the fast tidal currents that are stripping a portion of the estuary of its mud bottom in a process known as tidal scour.

Managed by the Elkhorn Slough Tidal Wetland Project, a collaborative, ecosystem-based effort led by the Elkhorn Slough National Estuarine Research Reserve and the Elkhorn Slough Foundation, the project is the culmination of more than six years of careful study by more than 100 scientists, resource managers, and conservationists, who first strived to understand the habitat changes that tidal scour and marsh dieback were causing in the estuary, and then designed an ecologically and fiscally feasible solution.

Saving the Salt Marsh

Brown Pelicans

Brown Pelicans convene at the Elkhorn Slough NERR, a stopover on the Pacific Flyway and a designated Globally Important Bird Area.

The underwater sill is expected to greatly diminish the tidal scour that washes thousands of cubic yards of sediment into the nearby Monterey Bay National Marine Sanctuary each year. Scientists estimate that over time, the saved sediments will increase the viability of tidal marsh at Elkhorn Slough, which was impacted by altered hydrology (water circulation) that led to a shortage of sediment and a rise in sea level relative to the marsh plain.

Preserving the estuary’s muddy habitats allows native marsh plants like pickleweed to trap sediment and flourish. It also sustains the sediment of eelgrass beds. Without them, the resident wildlife, from the federally endangered Santa Cruz long-toed salamander to the threatened southern sea otter, becomes deprived of food and habitat.

The only other solution – to truck in additional sediments – was cost-prohibitive to the tune of tens of millions of dollars.

An Extraordinary Ecosystem

Brown Pelican

A Brown Pelican in effortless flight.

The Elkhorn Slough NERR is an extraordinarily diverse ecosystem that comprises the second-largest estuary on the California coast (the larger one is San Francisco Bay). Its marine mammals include sea lions, harbor seals, and sea otters, and the area hosts 340 bird, 550 marine invertebrate, and 102 fish species – two dozen of them listed as rare, threatened, or endangered. As a stopover on the Pacific Flyway, the Slough is also a designated Globally Important Bird Area.  

The Slough’s creeks, mudflats, and salt marshes are also critical nursery grounds for many species, including sea otters, Caspian terns, leopard sharks, and bat rays. Recent research has found that some offshore species, such as sole, flounder, and halibut, also rely heavily on the estuary’s waters during their early development.

At the same time, the area supports an array of human pursuits. The Elkhorn Slough watershed hosts the largest electric power generating plant in California, is flanked by major transportation corridors, and produces a significant proportion of the state’s strawberry crop. Moss Landing Harbor, located at the entrance to the Slough, is one of the state’s most active fishing ports. Residential development pressures persist, while recreational activities, like boating, kayaking, and bird watching, have increased over the past decade. 

Better Habitat for All


The wide-ranging Whimbrel sports an impressively long curved bill.

It’s only fitting, then, that the new sill should improve the quality of life for people as well as wildlife in and around Elkhorn Slough. And so it has: The NERR identified more than 107 people who received paychecks as a result of the project, among them marine contractors, rock and steel vendors, water quality scientists, engineers, ecologists, and wildlife biologists. All of the engineering, permitting, and construction was conducted with input from the local community, while environmental monitoring ensured the wildlife’s well-being throughout the construction process.

The Elkhorn Slough NERR sill project came to fruition in a serendipitous melding of long-term study, careful planning, and a unique funding opportunity through the American Recovery and Reinvestment Act. The project embodies the mission of NOAA’s National Estuarine Research Reserve System, which is to promote the stewardship of coasts and estuaries through place-based living laboratories and “classrooms” where innovative research and management approaches can be applied to issues of local, regional, and national importance.

The lessons to be learned there – on tidal scour and erosion, their impacts on species, and mixed uses of the coastal zone – will no doubt be applied far and wide.

Other key partners in the sill project include the California Department of Fish and Game, Ducks Unlimited, URS Corporation, California Coastal Conservancy, David and Lucille Packard Foundation, and U.S. Environmental Protection Agency.