The San Dieguito River watershed is a drainage area of approximately 346 square miles in west-central San Diego County.  The watershed includes portions of the cities of Del Mar, Escondido, Poway, San Diego, and Solana Beach, and unincorporated San Diego County.  In terms of land area, the majority of the watershed (79.8%) is within the unincorporated jurisdiction.  The San Dieguito River watershed is presently divided into vacant/undeveloped (54%), parks/open space (29 %), and urban (18%) land uses.  Nearly half of the vacant land area is open to future development, most of which is zoned for residential usage.  The current watershed population is approximately 125,000 however; this level is projected increase to over 210,000 residents by 2015.

The watershed extends through a diverse array of habitats from its eastern headwaters in the Volcan Mountains to the outlet at the San Dieguito Lagoon and the Pacific Ocean.  There are several important natural areas within the watershed that sustain a number of threatened and endangered species.  Among these are the 55-mile long, 80,000 acre San Dieguito River Park, the 150 acre San Dieguito Lagoon, and five water storage reservoirs including Lake Hodges, Lake Sutherland, and Lake Poway.

The Pacific Ocean at the mouth of the San Dieguito River is listed as a 303(d)-impaired water body for elevated coliform bacteria.  In the absence of a comprehensive watershed planning effort, large-scale future development may exasperate current water quality problems and create additional beneficial use impairments.  The San Dieguito Lagoon is especially sensitive to the effects of pollutants and oxygen depletion due to restricted or intermittent tidal flushing.

There are many beneficial water uses within the San Dieguito Watershed as designated in the State Water Resources Control Board's San Diego Region Basin Plan.