Wetlands are among the most important and hardest-working ecosystems in the world, rivaling rain forests and coral reefs in productivity of life. 

They produce high levels of oxygen, filter toxic chemicals out of water, sequester carbon, reduce flooding and erosion, recharge groundwater and provide a diverse range of recreational opportunities from fishing and hunting to photography. They also serve as critical habitat for wildlife, including a large percentage of plants and animals on California’s endangered species list.

As the state grew into one of the world’s leading economies, Californians developed and transformed the state’s marshes, swamps and tidal flats, losing as much as 90 percent of the original wetlands acreage—a greater percentage of loss than any other state in the nation.

While the conversion of wetlands has slowed, the loss in California is significant and it affects a range of factors from water quality to quality of life.

Wetlands still remain in every part of the state, with the greatest concentration in the Sacramento-San Joaquin Delta and its watershed, which includes the Central Valley. While wetlands in all areas of the state are important, the Delta and related wetlands take on special significance because they are part of the vast complex of waterways that provide two-thirds of California’s drinking water.

Wetlands Overview

In general, California’s wetlands are the bogs, swamps, estuaries and marshes connected to streams, groundwater, rivers, lakes and coastlines. The majority of California’s wetlands are semi-aquatic links in a water-based chain extending from the Sierra Nevada mountain range to the Pacific Ocean.

Wetlands have their own unique ecosystems, which typically include specific types of soils supporting plants adapted to the soils and a watery environment. Despite their name, wetlands are not always wet, though characteristically, they experience periodic saturation.

Wetlands can be permanent or seasonal. Permanent wetlands tend to stay saturated with water, and in the case of tidal wetlands are flooded or drained twice each day. Seasonal wetlands such as tule fields and vernal pools experience saturation or flooding only part of the year. Even though water may be present only a few weeks out of every year, seasonal wetlands nonetheless share the soils, plants and animal life characteristic of permanent wetlands.

The vast majority of California’s wetlands are freshwater and found in bogs, marshes and swamps. The state has also significant coastal and tidal wetlands, and along lakes and rivers (known as riparian wetlands).

One acre of wetlands can filter 7.3 million gallons of water a year. You can see an example of a wetland in this video shot at San Luis National Wildlife Refuge in the San Joaquin Valley.

Many Californians are aware only of coastal and tidal wetlands, yet the majority of California’s wetlands lie in freshwater environments. Freshwater marshes occur in ponds and slow moving water.

In the Central Valley, wetlands — partly or seasonally saturated land that supports aquatic life and distinct ecosystems — provide critical habitat for a variety of wildlife. In 2021, new research reported by the National Audubon Society revealed that tens of millions of migratory birds depend on riparian and wetland habitat of the Central Valley as well as the Colorado River Delta.

Benefits of Wetlands

Essentially acting as a kidney system for the landscape, wetlands’ soil and vegetation filter water and absorb nutrients and contaminants. Other benefits of wetlands include:

• controlling floods
• recharging groundwater 
• controlling erosion 
• helping to stabilize shorelines
• mitigating the intrusion of salty seawater
• providing habitat for fish, waterfowl and other wildlife
• absorbing oxygen and carbon (and seen as a key carbon sink to help address climate change)

Looking Ahead

Wetlands are essential in fostering biodiversity within a broad ecosystem, and loss of wetlands has resulted not only in a loss of this diversity, but also in the extinction and endangerment of numerous species. Half of all animals and a third of all plants listed as endangered depend on wetlands.

Science has shown that California’s wetlands are part of a large, interconnected system and can be a tool in helping the state meet its carbon reduction mandate. To protect one element in it, all must be addressed. While protection of wetlands is a continuing emphasis, so are acquisition and restoration of wetlands. 

The state of California and the federal government have been at odds over how widely to define wetlands protections. The federal government and the U.S. Supreme Court have tended to narrow the definition of waters of the United States that are subject to the Clean Water Act.

In response, the State Water Resources Control Board sought to protect California’s non-navigable wetlands under the Porter-Cologne Water Quality Control Act. However, a 2021 Sacramento Superior Court ruling found that the state is not authorized to take such an action for wetlands that do not meet the federal definition of waters of the United States.