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

Carlsbad Watershed

Map of Carlsbad watershed


The Carlsbad Hydrologic Unit (HU) is approximately 210 square miles in area extending from the headwaters above Lake Wolhford in the east to the Pacific Ocean in the west, and from Vista and Oceanside in the north to Solana Beach, Escondido, and the community of Rancho Santa Fe to the south. The cities of Carlsbad, San Marcos, and Encinitas are entirely within this HU. There are numerous important surface hydrologic features within the Carlsbad HU including four unique coastal lagoons, three major creeks, and two large water storage reservoirs. The HU contains four major, roughly parallel hydrologic areas. From north to south they are the Buena Vista (901.2), the Agua Hedionda (904.3), the Batiquitos (904.5), and the San Elijo (904.6) HAs. Two smaller HAs, the Loma Alta (904.1) and the Canyon de las Encinas (904.4) are also within the Carlsbad HU.

The largest jurisdictions in terms of land area in the Carlsbad HU are the unincorporated San Diego County areas (66 sq. miles), the cities of Carlsbad (39 sq. miles) and San Marcos (24 sq. miles), and an approximately 27 square mile portion of the City of Escondido. The cities of Carlsbad, San Marcos, and Encinitas are located entirely within the HU. Approximately 48% of the Carlsbad HU is urbanized. The dominant land uses are residential (29%), commercial/ industrial (6%), freeways and roads (12%), agriculture (12%), and vacant/ undeveloped (32%).
Hydrologic Areas: Loma Alta, Buena Vista Creek, Agua Hedionda, Encinas, San Marcos, Escondido Creek
Major Water Bodies: Loma Alta Creek, Buena Vista Creek, Buena Vista Lagoon, Agua Hedionda Creek, Agua Hedionda Lagoon, San Marcos Creek, Batiquitos Lagoon, Escondido Creek, San Elijo Lagoon, and Lake Wolhford

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.