Aliso Creek Directive

Regulatory Background

On March 2, 2001 the San Diego Regional Water Quality Control Board ("Regional Board") issued a directive, by authority of California Water Code Section 13225, to the County of Orange, the Orange County Flood Control District, and the cities of Laguna Beach, Laguna Hills, Laguna Niguel, Laguna Woods, Lake Forest, Mission Viejo, and Aliso Viejo (Incorporated on July 1, 2001) to investigate urban runoff in the Aliso Creek watershed. The directive found that the "Permittees" may be discharging waste with high indicator bacteria concentrations from municipal stormdrain outfalls into Aliso Creek and its tributaries.

From 2001-2005 water samples from over 100 monitoring sites along Aliso Creek and its tributaries were tested weekly for indicator bacteria.

The Directive required the Permittees to:

  • Conduct weekly monitoring at all major outfalls to Aliso Creek
  • Evaluate the effectiveness of structural and non-structural Best Management Practices (BMPs) currently being implemented in the watershed and identify future measures that would eliminate levels of high bacteria from outfalls.

Recent Developments

The State Water Resources Control Board is proposing a statewide program to protect recreators from effects of pathogens in water.  The program includes chages to pathogen indicator bacteria and objectives for marine and fresh water. 


A brief description of efforts by the County and Cities since the Directive was issued is described below:

Data Collection and Reporting

From 2001-2005 water samples from over 100 monitoring sites along Aliso Creek and its tributaries were tested weekly for indicator bacteria. Many new BMPs were implemented to reduce bacteria levels in the watershed, including wetland restoration projects, a sand and clay filter/ultraviolet treatment system, increased street sweeping, illicit connection inspections, source investigations, and public education and outreach efforts.

On October 12, 2005, the Regional Board approved a new monitoring program due to a request from the Permittees, concluding that the proposed changes would constitute an effective interim program until adoption of the Beaches and Creeks Indicator Bacteria TMDLs which was accepted in February 2010.

The Revised Monitoring Program was based on the 13225 Directive monitoring data and improved knowledge about overall patterns of bacteria in the watershed and localized responses to specific BMPs. Current monitoring efforts focus on status and trends sites near the bottom of the watershed and BMP evaluation sites at high-priority drains throughout the watershed. Monitoring frequency increased relative to monitoring conducted in 2001-2005, but occurs only in summer when bacteria concentrations are highest. Orange County Health Care Agency publishes bacterial water quality monitoring data on its website.

Aliso Creek Watershed Revised Monitoring Program Sampling Locations

Findings of the Aliso Creek Revised Monitoring Program are compiled annually as part of the Aliso Creek Watershed Runoff Management Plan Water Quality Data Assessment annual report.  The annual reports are filed in the OC Public Works Document Library (to find the reports: in the Name column, type Aliso).  For additional information about the Aliso Creek Watershed, see the Aliso Creek Watershed page

On February 10, 2010 the Regional Board adopted TMDLs for indicator bacteria to address impaired beaches and creeks in the San Diego region (Beaches and Creeks Indicator Bacteria TMDLs) including Aliso Creek and its tributaries, the Aliso Creek Mouth, and Aliso Beach.  In addition to the Directive Monitoring efforts, management efforts on indicator bacteria have been generally shifted to the implementation of the Beaches and Creeks TMDL.

Contact Info

Jian PengSection Chief  | phone icon (714) 955-0650 |  envelope | all TMDLs

Stella Shao  | phone icon (714) 955-0651  |  envelope |
Aliso Creek, San Juan Creek; South County Coastal Area Indicator Bacterial (including Baby Beach), Newport Bay Sediment, Selenium TMDLs