Lake San Marcos

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Adjacent to the City of San Marcos, Lake San Marcos is an unincorporated area of San Diego County that occupies approximately 80 acres.

Water Quality

Agendas & Minutes


Documents & Plans

Agency Agreements 

Public Agency Workshop Group

Email Notifications

Lake San Marcos Water Quality

The San Diego Regional Water Quality Control Board (Regional Board) determined that San Marcos Creek and Lake San Marcos are impaired water bodies for nutrients (i.e. Ammonia, Nitrate, Nitrite, Total Kjeldahl Nitrogen, Orthophosphate, Total Phosphorous and etc.).

Designation of a water body and its offending pollutant as impaired means the water body is then placed on the State’s 303(d) list in order to reduce the amount of pollutants entering the water body to meet water quality standards.

  • Determining existing water quality conditions
    An outline of the proposed scope for investigative work in San Marcos Creek and Lake San Marcos will identify steps needed to determine existing nutrient water quality conditions and those sources contributing to this impairment. The results of this investigative work will enable the parties to undertake additional steps to abate the nutrients.

  • Nutrient Sources
    The suspected sources of these nutrients are diverse and may include activities associated with the: agricultural, commercial, construction, educational, industrial and municipal sectors of the community. However, at this time not all dischargers or sources of said nutrients have been identified. Certain parties, including several public agencies and various private parties, alleged to be responsible for these impairments, developed a voluntary process for diagnosing and abating such impairment conditions in coordination with the Regional Water Quality Control Board. 

  • Public Participation
    Although, Lake San Marcos is officially just outside of City limits it is an integral part of the community.

Transparency and public involvement is important element in developing meaningful and implementable solutions to complex issues. In order to ensure full transparency interested members of the public are invited to not only review all documents below, but also be involved in the process.

Agendas & Minutes

Lake San Marcos Public Workshop Agenda - Dec. 3, 2014


Lake San Marcos Public Workshop Presentation - Dec. 3, 2014
Lake San Marcos Public Participation Presentation - Jan. 31, 2013
Lake San Marcos Public Participation Plan Presentation - Jan. 18, 2012 
Lake San Marcos Public Participation Workshop Q&A Sheet - Jan. 18, 2012
Upper San Marcos Creek Watershed Nutrient Management Plan PowerPoint

Regulatory Documents & Plans

Public Participation Draft Plan - Oct. 11, 2011
Upper San Marcos Creek Watershed Nutrient Management Plan

Agency Agreement to Implement Phase 1 (Diagnostic Phase)

Participation Agreement Among the Lake San Marcos Workgroup - Final Executed OPA
Final Executed Cooperation Agreement
Water Quality Management in Lake San Marcos: Analysis of Available Data

Public Agency Workshop Group (PAWG)

PAWG Stormwater Hotline Numbers

Email Notifications

To receive official notices and related documents concerning the Lake San Marcos project, please use the following steps:

  • Visit the San Diego Regional Water Quality Control Board's website,, then navigate to a left link titled "Email Subscriptions."
  • Click "Email Subscriptions" and select Lake San Marcos. Enter your name and email address, then click subscribe.
  • You will receive an email from the State Board asking you to confirm e-notification sign-up. Upon replying reply to the confirmation email, you will be added to the notification list and receive Lake San Marcos updates.

 Stormwater Division
Stormwater Program Manager
1 Civic Center Drive
San Marcos, CA 92069
(760) 744-1050
Reed Thornberry
(760) 744-1050, ext. 3217