Oso Flaco Lake Watershed
Featured Project
Oso Flaco Lake and Little Oso Flaco Lake Non-Point Source Pollution Assessment
Oso Flaco and Little Oso Flaco Lakes are located in the western portion of the Santa Maria Valley in southern San Luis Obispo County, California. The Oso Flaco Creek watershed contains about 7,400 acres, nearly all of which consist of prime agricultural land. On average, 2½ crops per year are produced on these intensively cultivated fields. The primary crops are strawberries, lettuce, broccoli, cabbage, celery, cauliflower. The average annual rainfall is about 12 inches, most of which occurs from early November through mid-April. Groundwater is pumped for irrigation and applied to row crops through combinations of furrow, overhead sprinklers and drip irrigation.
The western terminus of the watershed is Oso Flaco Lake, the largest of the freshwater lakes associated with the 18-mile-long Guadalupe-Nipomo Dune Complex. These freshwater lakes occupy a surface area of 82 acres and are classified as palustrine emergent wetlands. The lakes and surrounding area are owned and managed by the California Department of Parks and Recreation, Oceano Dunes District. This area provides habitat to several threatened or endangered animals and California State species of concerns including the horned lark, least bell’s vireo, California red-legged frog, the western pond turtle, the California least tern, Gambell’s watercress, marsh sandwort, and beach spectacle pod.
Water quality in the Oso Flaco watershed has been found by the RWQCB to be impaired by several pollutants, including pesticides, nitrate and excessive sediment. In response to these concerns, in order to better inform management measures for Oso Flaco, since 2008 State Parks has contracted with the Coastal San Luis RCD to conduct water quality monitoring and streamflow measurements in Oso Flaco. The CSLRCD's monitoring includes collecting data from continuous sampling devices installed in Oso Flaco Creek and Oso Flaco Lake, and in addition collecting grab samples on a regular basis for laboratory analysis.
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