The Watershed System

Watersheds are complex systems of water, land, plants and wildlife. Healthy watersheds provide water for drinking, habitat, food, agriculture, industry and recreation.

The San Lorenzo Creek watershed has five main areas:

Grasslands These high elevations of the East Bay hills consist of grass, brush and chaparral. Soil there acts as a sponge, soaking up water and serving as a large earthen reservoir. Water stored is released slowly into creeks during the summer months.

Woodlands
These hilly areas are covered with stands of oaks. Soils here also act as a sponge and the trees provide habitat, shade and food, and filter pollutants from soil and air.

Creeks
The most fragile and biologically diverse areas of the watershed, creeks and the nearby land are called riparian areas. Native trees and brush along creeks provide shade that keeps the water cool enough for trout and steelhead. Plant roots hold the soil in place and reduce the flow of water so it can be absorbed into soil, providing natural flood protection. However, pollutants and soil erosion can harm riparian areas more quickly than they can be naturally purified. Some creeks were been channelized in concrete many years ago and provide little habitat value. However, modern engineering techniques can improve fish passage by incorporating resting pools and fish ladders to help fish make their way upstream to natural spawning areas.

Developed Areas
In urban and suburban areas, the natural drainage system is supplemented with a system of storm drains, mainly underground. Storm drains collect water from streets, roofs and other paved areas and send it directly to creeks and then to the Bay, without any cleansing treatment. Whether you live right next to a creek or miles away, water from rain, sprinklers and washing cars washes pollutants, trash, pet waste, car oils, pesticides and herbicides off yards, parking lots and streets into storm drains. The more paved, or impervious area, there is, the more untreated water goes to the Bay.

Wetlands
The mixing of fresh and salt water at the edge of the Bay creates a unique environment that supports a diversity of life including shore and wading birds, fish, shellfish and small mammals. Wetland plants provide the last filtering process for water before it enters the Bay. But herbicides in untreated water can kill plants and pesticides kill the insects that feed the birds and fish.