What is a Watershed?

A watershed is a geographic area in which all sources of water, including lakes, rivers, estuaries, wetlands, and streams, as well as ground water, drain to a common surface or water body. Watersheds are defined by the topography of the land. Since a watershed is made up of several components that are all part of the "big watershed picture," it is important to remember that what happens on the land can affect the water. For example, if a river or stream flows through an agricultural area, it can pick up fertilizer, manure, and pesticides from farming operations that run off the land after a rainstorm. As it passes urban and suburban areas, it might gather fertilizers that wash off lawns, untreated sewage from failing septic tanks, wastewater discharges from industrial facilities, sediment from construction sites, and runoff from impervious surfaces like parking lots. All of these land uses – agricultural, suburban, urban, and coastal –can have an impact on our fresh and marine waters. (Excerpted from the US EPA Office of Water, Publication EPA 842-F-98-006, "Your Coastal Watershed")

Water quality affects fish and other aquatic species. The native vegetation along stream banks, known as riparian habitat, helps filter pollutants from runoff. Additionally, riparian vegetation keep our streams cooled for fish and other species, and the forests serve as critical habitat for migrating and nesting birds. Yet over 90% of our riparian forests have been removed for land development activity and other uses. Additionally, since 1994 three of our most sensitive watershed species have been listed under the state and federal Environmental Species Acts: the Coho Salmon, Steelhead Trout, and California Red-Legged Frog--raising new concerns regarding the water quality of our streams.

A watershed is not just a scientific definition, it's a way of thinking about environmental management. Watersheds are a natural way to divide up an area into regions. By using watershed management we are looking at all the aspects of the ecosystem instead of managing one particular resource within the watershed. Watershed management is an effective way to protect the environment because it is interdisciplinary, using many different sciences to evaluate and make decisions about the environment. The Brazil Watershed Group uses this excellent definition of watershed management: " Watershed ecology is as much a philosophy as a scientific investigation. It is a purposeful search for communal awareness, that interconnectedness that ties together everything on and within this water planet. It integrates geology, hydrology, chemistry, biology, sociology, economics, history and art into a composite science that can transcend many artificial boundaries of academics. It is a complexity of perspectives that witnesses life as individuals and communities, cycles and flows, biofilms and biosphere."

Monterey Bay Watersheds

The central coast of California has over 11 watersheds which drain into the Monterey Bay National Marine Sanctuary, the nation's largest protected marine area and the second largest protected marine area on the earth (after the Great Barrier Reef in Australia). The Sanctuary's boundaries stretch 350 miles from Marin County to San Luis Obispo County, covering over 1/3 the coast line of the state and extending as far as 53 miles offshore. The sanctuary has been in place since 1992.

Source: Monterey National Marine Sanctuary

For more about watersheds:

Estuaries

Unique Animals

Riparian Plants