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MBAC tests water after rain to ensure safe conditions

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Why we sometimes cancel classes on sunny days and what you can do to help.

The water in Mission Bay is typically clean for swimming and watersports except in occasional situations due to rainwater runoff. While the City of San Diego has completed a multi-million dollar dry weather storm drain diversion system that has dramatically improved the water quality overall, there are times when the bay may contain unsafe levels of bacteria and other organisms like any other body of water subject to rainwater runoff.

Beaches and bays can become temporarily unsafe for contact following large amounts of rain that produce storm water runoff. This occurs when rain, and other sources of runoff, transport pollutants (animal waste, automotive fluids, cleaners, fertilizers, etc.) into storm drains or gutters that later make their way to the bay and ocean. During periods of dry weather storm drains are connected to the sewer system, however, during heavy rain overflow runoff is diverted directly to our beaches and other waters where we swim causing contamination and temporary closures until the bacteria returns to safe levels for contact. As the water circulates in the bay and ocean due to the tide, and the sun killing the bacteria in the water, the bay and ocean will return to normal levels and the closure is lifted. Swimming in contaminated water won’t always make you sick, but it does increase your chances of becoming ill if you are exposed.

The Mission Bay Aquatic Center conducts water testing in the vicinity of MBAC after periods of heavy rain to ensure the water is safe for contact. These tests take time for the samples to incubate, and the water takes time to return to normal levels following a large storm, thus the reason for closures on nice sunny days following a storm. The length of time necessary for the water to clear up following a storm is dependent on how much rain occurred, how long of a period of dry weather between storms for pollutants to build up before being washed into the bay, and other factors. Sometimes the water becomes safe enough for minimum contact sports such as sailing and kayaking, before becoming safe enough for full contact activities like wakeboarding. The ocean is typically cleared quicker than the bay due to the large volume of water and movement of the water. Each one of us can do our part to help keep our bay and ocean clean and keep closures to a minimum by:

  • Picking up trash and debris around your yard and home.
  • Regularly checking your vehicle for fluid leaks and keeping it serviced.
  • Carrying bags to pick up after your pet and disposing of pet waste in the trash.
  • When gardening use fertilizers and pesticides sparingly. Read labels carefully and only apply after it rains, not before.
  • Visit for more tips and simply changes you can make to keep our oceans blue.

We have been testing water quality in Mission Bay and Mission Beach for several years and have a lot of experience to generally know when the water will be unsafe, but we always complete water tests to ensure our customer’s safety. We will not allow classes to go in water that we know is contaminated.

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