Improving Water Quality in the Middle Santa Ana River Watershed

The Santa Ana River travels from the top of the San Bernardino Mountains, through Riverside and San Bernardino Counties, cuts into the northern Santa Ana Mountains, and eventually drains into the Pacific Ocean. At over 96 miles long, the Santa Ana River is the largest coastal stream system in Southern California. The drainage area surrounding the river creates the Santa Ana River Watershed.


Although the entire Santa Ana River Watershed covers 2,650 square miles, the tributary drainage area to the Middle Santa Ana River Watershed is 480 square miles. The Middle Santa Ana River Watershed is a unique area of land that includes open space, commercial, residential and agricultural use.

The state of California has nine Regional Water Quality Control Boards that oversee water quality and compliance for their own region. The Santa Ana Regional Water Quality Control Board (RWQCB) oversees the Santa Ana River Watershed, including the Middle Santa Ana River Watershed (MSAR). According to Section 303(d) of the Clean Water Act, the Regional Board is required to identify surface waters that fail to meet water quality standards. Once a body of water has been added to the 303(d) list as impaired, a Total Maximum Daily Load (TMDL) must be established for the waterbody as well as for the given pollutant.

Due to high densities of bacterial indicators, several bodies of water in the Middle Santa Ana River (MSAR) Watershed have been included on the 303(d) list of impaired waterbodies. To address the concerns of fecal coliform bacterial indicators, the RWQCB included the formation of the Middle Santa Ana River TMDL Task Force. Overseen by the Santa Ana Watershed Projects Authority (SAWPA), this task force includes 18 stakeholders working together with the RWQCB to improve the water quality of the MSAR.


Since beginning in 2006, the MSAR Watershed TMDL Task Force continues to address water quality issues by conducting on-going source investigation to identify bacterial indicators and understand how to solve them. In addition to monitoring, TMDL tasks include preparing progress reports, implementing an Urban Source Evaluation Plan, revising a Comprehensive Bacteria Reduction Plan (CBRP) and a Water Quality Management Plan (WQMP) for both Riverside and San Bernardino Counties. The TMDL Task Force has conducted over 20 water quality monitoring projects


Due to the success of the Task Force, some waterbodies throughout the MSAR have had such high levels of bacteria load reductions that they are no longer considered impaired. The Comprehensive Bacteria Reduction Plan (CBRP) that was introduced in 2012 has shown a 66% reduction in fecal bacteria loads. The MSAR Bacterial Indicator TMDL set limits on waste for urban Municipal Separate Storm Sewer Systems (MS4) and confined animal feeding operation dischargers, load allocations for agricultural and natural sources.

The significant improvements being made to the Middle Santa Ana River are a collaborative effort between the RWQB, the Santa Ana Watershed Projects Authority, as well as the several agencies involved. With the TMDL in place, impaired waterbodies are monitored until water quality is fully restored. To find out more about the MSAR TMDL Task Force, visit