Lower Tijuana River Indicator Bacteria and Trash Advance Restoration Plan

Background Information

The Tijuana River watershed is in the southernmost portion of the San Diego Water Board’s jurisdiction. Divided by the United States-Mexico international border, approximately one-third of the watershed is in the United States and two-thirds is in Mexico. In the lower watershed, the river and several of its tributaries cross from Mexico into the United States; these transboundary flows act as conduits for pollution generated in Mexico, transporting them through the river valley, estuary, and into the Pacific Ocean.

The lower Tijuana River refers to the stretch of the river that crosses the border from Mexico into the U.S., traverses the Tijuana River Valley and the Tijuana River Estuary, and ultimately reaches the Pacific Ocean. For decades, this stretch of river has not met water quality standards due to routine and episodic transboundary flows from Mexico, often comprised of untreated domestic and industrial wastewater.

Project Description

The San Diego Water Board developed the Lower Tijuana River Indicator Bacteria and Trash Advance Restoration Plan (ARP) to address water quality impairments through an implementation plan with actions to restore and maintain water quality standards. Waters with an ARP remain on the Clear Water Act 303(d) List until water quality standards are attained. Board staff developed the ARP in response to direction from the San Diego Water Board to identify a plan for water quality restoration to address impairments to human and wildlife beneficial uses of water in and around the lower Tijuana River due to high levels of bacteria and trash.

The ARP identifies sources of trash and indicator bacteria pollution, establishes numeric targets to achieve water quality standards in the river, and identifies potential actions for pollution control in an implementation plan. The ARP is centered on the expectation of the San Diego Water Board that the U.S. Section of the International Boundary and Water Commission (USIBWC) will work with the U.S. Environmental Protection Agency (USEPA) to implement the core and supplemental projects identified in the June 9, 2023 USIBWC-USEPA Joint Record of Decision to significantly reduce indicator bacteria and trash loads in transboundary flows.

Although the Tijuana River is on the 303(d) List for impairments due to a total of 20 pollutants, control of the sources of indicator bacteria and trash is likely to result in a significant degree of control of the remaining pollutants. Pollutants that are conveyed to the lower Tijuana River by dry weather and wet weather flows are generally intermingled. Reduction of indicator bacteria requires reduction of sewage and polluted urban runoff entering the Tijuana River Valley. Therefore, the loads and concentrations of other pollutants inherent in sewage and polluted urban runoff would also be reduced.

The San Diego Regional Water Quality Control Board (San Diego Water Board) adopted Resolution R9-2024-0155 on December 11, 2024, approving the Lower Tijuana River Indicator Bacteria and Trash Advance Restoration Plan.

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