Freshwater Marsh

The Sacramento-San Joaquin Delta (Delta) is known the world over as a prime agricultural area, supporting profitable export crops such as rice, almonds, tomatoes, and pears. Historically, however, the area looked very different. Before the reclamation efforts in the mid- to late 1800s, the Delta was dominated by vast areas of freshwater tidal marsh. Tule (Scirpus spp.) filled most of the matrix and grew everywhere except in the deeper water channels and along thin corridors where riparian trees took hold. Reclamation of land for development and agriculture led to the construction of levees that channelized Delta waterways and cut off surrounding lands from their traditional floodplains. Today, less than 2 percent of the original marsh habitat remains.

Fascinating Features

  • Prior to development, almost half of California’s coastal wetlands were located within the Delta.
  • The largest species of gartersnake, the giant gartersnake (Thamnophis gigas), relies on freshwater marsh, where it hunts frogs, fish, and other small critters. Giant gartersnakes can grow to be more than 5 feet long and are listed as endangered, in large part because of loss of marsh habitat.
  • Most soils are derived from the weathering and erosion of rock minerals, but peat soils in the Delta—which are prized for agriculture—were formed over thousands of years by the decaying wetland plants, mostly tules.

Habitat Values

Freshwater marshes perform important ecological services, such as increasing water storage; reducing river flow velocity; trapping sediment from runoff, which improves downstream water quality; reducing wave action that can threaten Delta levees during high flow events; and sequestering carbon that would otherwise contribute to global warming. In the Delta, marshes also provide valuable fish and wildlife habitat.

Native fish habitat

Fish such as Chinook salmon (Oncorhynchus tshawytscha), delta smelt (Hypomesus transpacificus), steelhead (Oncorhynchus mykiss), and sturgeon (Acipenser spp.) use freshwater marshes as critical nursery grounds, where young fry can feed on plentiful resources before migrating out to the Pacific Ocean.

Migrating bird habitat

Sandhill Cranes (Antigone canadensis) and many species of ducks and geese count on the remaining wetlands as important wintering grounds in the Pacific Flyway.

Native plant habitat

Delta freshwater marsh also supports many plant species that are found nowhere else, such as the Suisun Marsh aster (Symphyotricum lentum), Delta tule pea (Lathyrus jepsonii var. jepsonii), and woolly rose mallow (Hibiscus lasiocarpos var. occidentalis), which is the official plant of the Sacramento Valley Chapter!

Places to Visit

There are several locations within the Delta and around the Sacramento Valley that are open to the public, where you can see and learn about freshwater marsh habitat for yourself.  Here are a few of our suggestions.