Newport Bay Nutrient TMDL

The Newport Bay watershed covers an area of 154 square miles in central Orange County, some 77% of which is drained by the San Diego Creek subwatershed.

Excess nutrients flowing into the Bay, primarily from San Diego Creek, have resulted in seasonal algae blooms that have impaired the Bay’s environment and our enjoyment of this important natural resource. The nutrients of concern are nitrogen and phosphorous, which are both essential for plant growth and necessary for healthy ecological functions in the Bay.

However, high nutrient concentrations can cause excessive plant growth, including algae. This can lead to a problem called eutrophication, a condition in which excessive plant growth from nutrient enrichment impairs the capacity of a waterbody to sustain healthy ecological functions. This can lead to aesthetic problems, habitat loss, and poor biological diversity, among other adverse effects. Both nitrogen and phosphorous occur in nature, but eutrophication usually results from human activities that promote the input of these nutrients into our waterbodies. Some sources of these nutrients include agriculture, excessive garden or lawn fertilization, and pet waste.

Photo of a sampling site in Upper Newport Bay in summer 1996,

In 1998, the Santa Ana Regional Water Quality Control Board adopted a Total Maximum Daily Load for nutrients in the Newport Bay watershed (TMDL) to decrease the mass of nutrients flowing into the Bay, thus restoring and protecting its beneficial uses. Beneficial uses are assigned to every water body in the United States as a means of systematically assessing the quality of the nation’s surface waters, as required by the federal Clean Water Act of 1972 . If a water body’s beneficial uses are impaired, then the water body is deemed impaired and requires restoration measures. The TMDL establishes maximum nutrient loads (targets) at levels similar to those observed in the 1970s, prior to observations of eutrophic conditions. Thus, if these targets are met, signs of eutrophication in the Bay should diminish.

Photo of the same site as above in summer 2009, showing the

In February 2000, a Regional Nutrient Monitoring Program (RMP) for the Newport Bay watershed was initiated by 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), as mandated by the TMDL to assess compliance with the required nutrient reductions. The RMP is composed of routine and special monitoring components. The routine monitoring component consists of weekly, bi-weekly, or monthly collection of water samples from sites throughout the watershed and monthly collection of algae samples from Upper Newport Bay.  Results from water quality and flow monitoring are published quarterly in the Newport Bay Watershed Nutrient TMDL Quarterly Data Reports (filed in the OC Public Works Document Library).   The special monitoring component is comprised of other studies to improve our understanding of nutrient sources and dynamics in the Bay. Data collected through the RMP are compiled into quarterly reports (formerly annual reports) to the Santa Ana Regional Board.

There are several other initiatives underway in the watershed to help improve water quality. Plant nurseries represent the largest form of agriculture still remaining in the County and formerly contributed large inputs of nutrients into the watershed from their runoff. Today, many of these nurseries capture and reuse most or all of their irrigation water, which has substantially reduced nutrient inputs. In addition, the Irvine Ranch Water District operates a natural treatment system, the San Joaquin Marsh, which helps remove many nutrients from San Diego Creek before it empties into Newport Bay.

You can help in efforts to restore Newport Bay. You might think that one person can do little to help the health of Newport Bay, much less our planet, but if we all did a little bit, we can have a great impact.