In 1998, the Santa Ana Regional Board adopted an amendment to the Water Quality Control Plan for the Santa Ana River Basin (Basin Plan) to establish a Total Maximum Daily Load (TMDL) for nutrients in the Newport Bay/San Diego Creek Watershed (Resolution No. 98-9, as amended by Resolution No. 98-100).

Nutrient loading to the Bay, particularly from the San Diego Creek watershed, has resulted in seasonal algae blooms in the Bay that impair the Bay’s recreation, navigation, and habitat beneficial uses. The TMDL was adopted to promote management efforts to restore and protect these beneficial uses in the Bay. It establishes targets for reducing the annual loading of nitrogen and phosphorus to Newport Bay by 50% and meeting the numeric and narrative water quality objectives by 2012. To achieve these targets, the TMDL establishes a number of interim targets requiring a 30% and 50% reduction in nutrients in summer flows by 2002 and 2007, respectively, and a 50% reduction in non-storm winter flows by 2012. The Nutrient TMDL allocates the allowable loads among identified nutrient sources, such as nurseries, groundwater dewatering facilities, urban runoff, agricultural discharges, as well as undefined sources (open spaces, atmospheric deposition, groundwater, etc.).

In February 2000, the County of Orange, on behalf of the watershed cities (Costa Mesa, Irvine, Laguna Hills, Laguna Woods, Lake Forest, Newport Beach, Orange, Santa Ana, and Tustin), initiated the Regional Nutrient Monitoring Program (RMP) for the Newport Bay and its watershed pursuant to the requirements established by the Santa Ana Regional Board (Resolution 99-77 to establish an RMP pursuant to the TMDL).

The RMP is composed of two components: a routine monitoring component and a special monitoring component. The routine monitoring includes most of the traditional monitoring that has occurred in the watershed (i.e. 24 hour composite samples collected either weekly, bi-weekly, or monthly from drainages throughout the watershed). The sampling locations are:

• Santa Ana-Delhi Channel at Irvine Boulevard
• San Diego Creek at Campus Drive
• Bonita Canyon Creek at MacArthur Boulevard
• Costa Mesa Channel at Westcliff
• El Modena-Irvine Channel at Michelle
• Lane Channel at Jamboree
• Agua Chinon Wash at Irvine Center Drive
• Peters Canyon Wash at Barranca
• San Diego Creek at Culver

The data collected from this routine monitoring is used to assess progress in the attainment of the interim and final TMDL targets for total nitrogen and total phosphorus loadings to the Bay. At present, the current loadings are meeting the interim targets. The results of the routine monitoring component can be found in the Annual Reports below. The special monitoring includes investigations to better understand the nature of nutrient sources and dynamics in the watershed. In addition, algae samples are collected from Upper Newport Bay to analyze the extent, magnitude, and duration of algal blooms.

Nutrient TMDL Documents

Quarterly Data Reports

Annual Reports

Special Studies