San Diego Coastkeeper


History
Mission Bay is a prominent feature of the San Diego coastline. This shallow, mesotidal estuary covers approximately 1862 ha (4600 acres) and has been modified extensively from its original appearance. Historically, Mission Bay was an estuary of the San Diego River and was dominated by tidal salt marsh and mud flats. Beginning in the late 19th century, the bay was developed as a recreational and commercial resource for the City of San Diego, and it now constitutes the largest aquatic park on the west coast of the United States. The San Diego River was separated from the Mission Bay inlet by a permanent dike in the late 1940s, and the bay subsequently was dredged and reshaped to alter the circulation and create islands.

Designated beneficial uses include water recreation, commercial and sport fishing, shellfish harvesting, spawning, migration, marine habitat and wildlife habitat.

Ecosystem health
San Diego Coastkeeper, the University of San Diego’s Marine and Environmental Studies Department and other project partners have conducted a comprehensive study to evaluate the impact of urban runoff on the bays’ water quality, sediment quality, planktonic and benthic communities. Findings show that Mission Bay contains three separate zones, each with their own residence times for impacts introduced by urban runoff, including fertilization of surrounding and residential lawns, irrigation and bacterial inputs.

Residence times refer to the amount of time that pollutants remain in a contained body of water. Since Mission Bay is partially contained, it can be separated into three distinct Zones, each with its own specified residence time. The greater the influence with the ocean, which acts as a mixing and flushing force on water quality in Mission Bay, the lower the residence time.

  • Zone 1 – Low residence times: Ventura Point
  • Zone 2 – Medium residence times: Fiesta Bay / Sail Bay
  • Zone 3 – High residence times – Eastern portion: Tecolote Creek Inlet / Cudahy Creek Inlet / Rose Creek Inlet (one to two weeks for introduced pollution to dissipate or be flushed out)

Conclusions
Human impacts to the Mission Bay ecosystem and water quality are numerous. In order to protect beneficial uses, agencies and community members need to minimize pollutant influx to the water body; in particular the Zone 3 areas that retain pollution for longer times. The main sources of pollution into this Zone are from the incoming creeks – Tecolote, Rose and Cudahy. Storm water and surface water run-off provide the greatest amount of pollution entering Mission Bay. Ways for residents and businesses to minimize their impact on storm water / surface water / urban run-off include:

  1. Do not over irrigate (www.bewaterwise.com has some great information)
  2. Apply fertilizers, pesticides only when needed and do not exceed dosages indicated on packages
  3. Wash your car on your lawn so that dirty water and detergents are absorbed by the grass in your front yard. Otherwise, all the soap, dirt and grease will flow into the stormdrain and directly to the ocean.