Santa Margarita River Estuary


The Santa Margarita River Watershed (Watershed) is located along the border between San Diego and Riverside Counties and drains to the Pacific Ocean just north of the City of Oceanside. The San Diego Regional Water Board is working collaboratively with stakeholders in the Watershed to complete special studies. These studies will help identify implementation plans to address impaired water bodies, and select the most appropriate regulatory tool(s) to restore beneficial uses. Although this is a watershed-wide effort, the initial focus is on the Santa Margarita River Estuary (Estuary).

The Estuary was placed on the 303(d) list in 1986 for eutrophic conditions. Eutrophic conditions cause dissolved oxygen concentrations to fall below 5 mg/l, making it difficult for the Estuary to support healthy aquatic life. The eutrophic condition of the Estuary is the result of excess nutrient inputs causing overabundant algal growth and the algal life cycle consuming more oxygen than it produces. Nutrients (Total Nitrogen and Total Phosphorus) discharged into the Estuary from the surrounding Watershed stimulate excessive algal growth. Two sources of nutrients to the Estuary, treated sewage and groundwater dewatering from a transit project, have been eliminated. The current focus in reducing eutrophication is to begin Early Actions (using existing regulatory authority to address sources) and to select the most appropriate regulatory tools for addressing the remaining upland sources of nutrients, mainly urban and agricultural runoff.

303(d) Listings

Public Documents

Public Meetings

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