TMDLs and ARPs Adopted by Regional Board

What is a TMDL?

A Total Maximum Daily Load (TMDL) is a science-based estimate of how much of a specific pollutant a waterbody can receive without harming its intended uses (called beneficial uses) — such as recreation, wildlife habitat, or drinking water supply. It serves as a planning tool to guide efforts to restore water quality by identifying both natural and human-caused sources of pollution. The federal Clean Water Act requires States to establish TMDLs when certain conditions are met for waters in which the State has identified impaired beneficial uses due to water pollution.

TMDLs assign allowable limits to controllable sources—such as stormwater discharges or wastewater treatment plants—so that the total pollution load stays within safe limits. This process is often referred to as a TMDL investigation and may lead to updates in the region’s official water quality plan (called the Basin Plan) or guide other actions to fix the problem sooner.

What Is an Advance Restoration Plan (ARP)?

An Advance Restoration Plan (ARP) can be a more efficient way to addressing water pollution. It works well when the problem appears to be related to better implementation of existing permits or when pollution is not the sole or main cause of the water quality problem.

An ARP includes:

• A clear schedule
• Specific milestones
• Targeted actions to reduce pollution

If the ARP successfully restores the water body, a formal TMDL may no longer be needed.

Why It Matters

Some rivers, lakes, and coastal waters in the San Diego Region don’t meet water quality standards and are considered “impaired.” Under the Clean Water Act, the state must identify these waters and develop TMDLs to address the impairment unless an alternative approach (like an ARP) is expected to achieve water quality standards more efficiently.

The San Diego Water Board’s TMDL Program works to:

• Restore and protect local rivers, lakes, and coastal waters (i.e. beaches)
• Coordinate with local, state, and federal partners
• Strengthen existing pollution control programs

TMDLs don’t replace current programs — they help us understand what’s working, what’s not, and how we can do better.

TMDLs and ARPs Adopted by Regional Board

Below is a list of adopted TMDL projects and approved ARPs. Click on the links to view documents, notices and other materials related to each project.

Additional Information and Links:

The State Water Resources Control Board (State Water Board) coordinates the TMDL Program statewide. The State Water Board's webpage contains addition information regarding the TMDL Program, development of TMDLs, and adopted TMDLs in California.

The Surface Water Ambient Monitoring Program (SWAMP) is a program run by the State Water Board that collects and shares scientific data about rivers, lakes, and streams.

The Surface Water Quality Assessment Program prepares a report every two years on the condition of California’s surface waters — including rivers, streams, reservoirs, estuaries, lagoons, bays, and ocean waters. This report is called the Integrated Report. It includes information about impaired waters and high-quality waters.

The U.S. Environmental Protection Agency (USEPA) has a webpage on the Impaired Waters and TMDL Program under section 303(d) of the Clean Water Act. Information on this page includes: status of 303(d) lists, TMDL program documents, TMDL Federal Advisory Committee, TMDL lawsuit information, and other links.