Total Maximum Daily Loads (TMDLs)

The Federal Clean Water Act Section 303(d) requires that States identify waters that do not or are not expected to meet water quality standards (beneficial uses, water quality objectives and the antidegradation policy) with the implementation of technology-based controls. Once a waterbody has been placed on category 5 of the 303(d) list of impaired waters, states are required to develop a Total Maximum Daily Load (TMDL) to address each pollutant causing impairment. A TMDL defines how much of a pollutant a waterbody can tolerate and still meet water quality standards. Each TMDL must account for all sources of the pollutant. TMDLs allocate allowable pollutant loads for each source, and identify management measures that, when implemented, will assure that water quality standards are attained.

More information on the on TMDLs and their development can be found on the State Water Resources Control Board website.

All TMDLs that have been adopted by the Santa Ana Regional Water Quality Control Board and approved by the Environmental Protection Agency (EPA) can be found in Chapter 6 of the Santa Ana Regional Water Quality Control Board’s Water Quality Control Plan (Basin Plan).

TMDL programs by watershed

Big Bear Lake, located in the San Bernardino Mountains, was created by the construction of the Bear Valley Dam in 1884. The Lake has a surface area of approximately 3,000 acres, a storage capacity of 73,320 acre-ft. and an average depth of 24 feet. The lake reaches its deepest point of 72 feet at the dam. The Big Bear Lake drainage basin encompasses 37 square miles and includes more than 10 streams. A TMDL for Total Phosphorus was adopted for dry hydrological conditions at Big Bear Lake on April 21, 2006. It was then approved by The Office of Administrative Law (OAL) on August 21, 2007 followed by the US Environmental Protection Agency (USEPA) on September 25, 2007. More information including the Implementation Plan can be found in Chapter 6 of the Santa Ana Water Board Basin Plan. Contact: Lauren Hubbell

The Middle Santa Ana River (MSAR) watershed covers approximately 488 square miles and lies largely in the southwestern corner of San Bernardino County, and the northwestern corner of Riverside County. A small part of Los Angeles County (Pomona/Claremont area) is also included. This watershed is comprised of three sub-watersheds: the Chino Basin watershed, the Riverside watershed, and the Temescal Canyon watershed.

Of the waterbodies listed on the Clean Water Act Section 303(d) list of impaired waters, the MSAR watershed currently has TMDLs for the following waterbodies

Middle Santa Ana River Bacteria TMDL

Lake Elsinore Canyon Lake nutrient TMDLs
The Lake Elsinore/San Jacinto River watershed is located in Riverside County and includes the following major waterbodies: Lake Hemet, San Jacinto River, Salt Creek, Canyon Lake and Lake Elsinore. The total drainage area of the San Jacinto River watershed is approximately 782 square miles. Over 90 percent of the watershed (735 square miles) drains into Canyon Lake. Lake Elsinore is the terminus of the San Jacinto River watershed. TMDLs for nutrients were adopted on December 20, 2004 for Lake Elsinore and Canyon Lake through Resolution R8-2004-0037. They were then approved by the US Environmental Protection Agency on (US EPA) September 30, 2005. More information can be found in Chapter 6 of the Santa Ana Water Board Basin Plan.


Contact: Lauren.Hubbell

The Newport Bay watershed is located in Central Orange County in the southwest corner of the Santa Ana River Basin, about 35 miles southeast of Los Angeles and 70 miles north of San Diego. The watershed encompasses 154 square miles and includes portions of the Cities of Newport Beach, Irvine, Laguna Hills, Lake Forest, Tustin, Orange, Santa Ana, and Costa Mesa. Mountains on three sides encircle the watershed; runoff from these mountains drains across the Tustin Plain and enters Upper Newport Bay via San Diego Creek.

Of the waterbodies listed on the Clean Water Act Section 303(d) list of impaired waters, the MSAR watershed currently has TMDLs for the following waterbodies

Newport Bay Fecal Coliform TMDL

December 2, 2022- Regional Board Hearing

 On December 2, 2022, the Santa Ana Regional Water Quality Control Board adopted Resolution No. R8-2022-0012 to incorporate Copper Total Maximum Daily Loads (TMDLs) for Newport Bay, Orange County, California into the Water Quality Control Plan for the Santa Ana River Basin (the Basin Plan Amendment).

 

August 5, 2025- State Water Board Hearing

The State Water Resources Control Board approved the Basin Plan Amendment under Resolution No. 2025-0023 on August 5, 2025

April 28, 2026 – OAL Approval

On April 28, 2026, the Office of Administrative Law approved the Regulatory Provisions for the Newport Bay Copper TMDLs (OAL Matter Number: 2026-0318-05S) pursuant to section 11353 of the Government Code. The Regulatory Provisions were endorsed and filed in the office of the Secretary of State of the State of California on April 28, 2026.

Next Steps

The Basin Plan Amendment incorporating the Copper TMDLs for Newport Bay will be submitted to the United States Environmental Protection Agency for review and approval. Portions of the Basin Plan Amendment not requiring USEPA approval are in effect for purposes of state law.

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Visit our subscription page to sign up to receive updates on the Newport Bay Copper TMDLs. Look for the section entitled “Total Maximum Daily Load (TMDL)” and check the box for “Newport Bay Cu / Metals -TMDL”.

For more information on the Copper TMDL, visit Copper TMDLs | Santa Ana Regional Water Quality Control Board. Please direct questions to Lauren Hubbell at lauren.hubbell@waterboards.ca.gov or (951) 320-6375.

Contacts

Regional Programs Section
Jagroop.Khela@waterboards.ca.gov
(951) 782-3288
Environmental Program Manager I (Supervisor)