WATER QUALITY MONITORING

Though you may not think of our local creeks as places you would encounter an abundance of fish, there are still fish in Bay Area streams! You might see steelhead trout, which are an anadromous species of fish meaning they are born in freshwater, travel to the ocean to mature, and return to freshwater streams to spawn offspring. Local creeks also host coastal roach, Sacramento sucker, and three-spined stickleback among others.

Our local creeks are also important migration corridors for wildlife, providing a sheltered linkage between upper watershed open space and the baylands below. You may see a gray fox among the trees, a great egret hunting for prey, or hear Pacific chorus frogs chirping. Many birds utilize the continuous canopy of native oaks, buckeyes, willows, and other trees that still exist along local creeks.

Turbidity

Turbidity measured in NTU (nephelometric turbidity units), is a measure of how murky water is. Throughout the year, most Mediterranean streams have low turbidity (e.g. clear water) with the exception of winter floods that cause high turbidity due to land runoff and increased flows. Water released from dams can have high turbidity, carrying sediments like silt and clay downstream. These deposits can bury cobble beds in the creek, decreasing spawning habitat for fish and refugia for aquatic invertebrates (4).

Dissolved Oxygen (DO)

Dissolved oxygen, measured in mg/L (milligrams per liter) and % (percent) saturation, refers to the amount of oxygen mixed in water. Almost all aquatic life needs oxygen in water to live. Eutrophication—the depletion of dissolved oxygen due the decay of algal blooms fueled by high nutrient runoff such as fertilizer— can cause massive die-off in aquatic life. Fresh cold water habitat should have a minimum dissolved oxygen of 7.0 mg/L and fresh warm water habitat should have a minimum of dissolved oxygen of 5.0 mg/L (1).

Trash

Trash, discarded waste from humans, is another pollutant that is monitored in creeks. Trash can be introduced to creeks directly, or be deposited from rains carrying urban runoff or wind carrying lightweight trash from land. Illegal dumping and careless disposal of waste degrades habitat, poisons wildlife, and can cause serious diseases.

Nitrates

San Francisquito Creek

The upper portion of the San Francisquito Creek watershed begins in the Santa Cruz Mountains. There are three main tributaries (smaller streams that flow into a larger body of water) that feed into the main stem of San Francisquito Creek: Los Trancos Creek, Corte Madera Creek, and Bear Creek. These waterways flow a combined 33 miles through Portola Valley, Woodside, Menlo Park, Palo Alto, and East Palo Alto and eventually drain into the San Francisco Bay.

Steelhead trout can still be found in the watershed but encounter many challenges. The Searsville Dam in Jasper Ridge Biological Preserve prevents steelhead from reaching upper watershed spawning grounds on the Corte Madera Creek tributary. Fortunately, other smaller migration barriers in the lower watershed have been removed over the years, and fish can still access the upper watersheds of the Bear Creek and Los Trancos Creek tributaries. Although the lower portion of the creek was never channelized in concrete like other creeks in the area, its flow is severely limited in drought years and the lower reaches of the creek are typically dry for much of the year.

Adobe Creek

Adobe Creek begins at the Black Mountain summit of the Santa Cruz Mountains, winding through Los Altos Hills, Los Altos, and Palo Alto on its way to the Palo Alto Flood Basin and the San Francisco Bay. Most of the upper watershed land is owned by the nonprofit Hidden Villa and the Midpeninsula Open Space District. On its journey, it travels 14.2 miles, meandering through community parks, and under Highway 101.

Steelhead trout have not been spotted on Adobe Creek since the late 1980s, but other native fish including California roach, Sacramento sucker, three-spined stickleback, and prickly sculpin have been found in the creek more recently. The loss of steelhead trout is due to multiple factors including partial fish passage barriers, loss of flow due to wells, diversions for irrigation, channelization of the lower creek, and periodic closure of the tidal gate in the Flood Basin.

In 2000 low oxygen conditions in the lower watershed caused a fish die-off, prompting the City of Palo Alto to begin a volunteer monitoring program of the creek, now run by Grassroots Ecology.

Matadero Creek

Matadero Creek’s course begins near Altamont Road and Black Mountain Road in Los Altos Hills. It passes through Palo Alto Hills before entering a concrete channel at El Camino Real that leads the creek through Midtown Palo Alto, and under Highway 101 to the Palo Alto Flood Basin.

Steelhead trout historically swam through Matadero Creek’s waters, but have not been reported there since the late 1980s.

Stevens Creek

Stevens Creek begins in the Santa Cruz Mountains in Monte Bello Open Space Preserve. It flows southward along the San Andreas fault line until it reaches Stevens Creek County Park at which point it changes direction and flows northward through Cupertino, Los Altos, Sunnyvale, and Mountain View before finally draining into the San Francisco Bay.

Stevens Creek serves as a critical habitat for steelhead trout (6). However, the Stevens Creek reservoir dam is a major fish barrier, and releases water downstream that is low in dissolved oxygen and high in temperature and turbidity. In Stevens Creek, waters with no oxygen lead to toxic methylmercury bioaccumulation, poisoning all life that make the creek their home (7). Consistently turbid water also decreases the quality of fish habitat by adding sediment that buries cobbles, decreasing egg laying locations and habitat for aquatic insects that are the food source of fish.