San Diego Citizen Watershed Monitoring Consortium Saturday, 11th October 
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SDCWMC > Watersheds

San Luis Rey Watershed

Map of San Luis Rey watershed


The San Luis Rey River watershed is located east of the City of Oceanside in the northwestern portion of San Diego County. The 558 square mile drainage is the largest hydrologic unit in the San Diego region. The watershed drains to the Pacific Ocean to the west and is bounded by the Moserate Mountains to the north, the Cleveland National Forest and Camp Pendleton to the northwest, and Escondido, San Diego, and other cities to the south. The basin is roughly 50 miles long by 16 miles wide, and is divided into two hydrologic units by Henshaw Dam. The areas above and below the dam encompass 206 and 354 square miles, respectively (USACOE, 1977).

Approximately 92.5% of the San Luis Rey River watershed is located in unincorporated areas of San Diego County. Roughly one-fourth of the land area in the watershed is located west of Interstate 15 including portions of the cities of Oceanside and Vista, the communities of Fallbrook and Bonsall, and the southwestern portion of Camp Pendleton. The land west of I-15 has multiple uses including open space/ undeveloped, residential, commercial/ industrial, and agricultural. East of Interstate 15, most of the land is owned and managed by government agencies (county, state, and federal), special districts, and Native American bands. The predominant land uses are open space/ undeveloped and agricultural.
Hydrologic Areas: Lower San Luis, Monserate, Warner Valley
Major Water Bodies: San Luis Rey River and Lake Henshaw

If you would like to select one of these major water bodies as your collection site, follow these instructions to get the information you will need for the registration form:

  • Copy the name of the water body (e.g., San Marcos Creek).
  • Go to www.topozone.com and paste the water body name in the place name field.
  • Select CA and click the Search button. The results will look similar to the screenshot below:
    www.topozone.com results for San Onofre Creek

    The information you will need to write down or copy from the results are:

    • Type: the water body type.
    • USGS Quad: the Nearest City field on the registration form.
    • Lat: the latitude.
    • Lon: the longitude.
  • Enter the information into the Collection Site Information section of the registration form.

If you need assistance in selecting a collection site, please contact us. We'll be happy to help you find a site that's as close to your group' or school's location as possible.