SAN FRANCISCO (KCBS)— A new mobile device app has been developed that lets people know if it is safe to go into the water at San Francisco beaches.

Along with help from the Dolphin Swim Club and the Surfrider Foundation, the city developed the app to measure if bacteria levels at the beach are safe.

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Surfers and swimmers alike can hit up 14 beaches along the city’s shoreline that are monitored by scientists on a weekly basis. Patrons of places like Ocean Beach and Aquatic Park may be interested in downloading the app for their iPhone or from Google Play for their Android.

Jean Walsh with the San Francsico Public Utilities Commission said the app is free and available to the public.

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The app has a simple green, yellow, or red light that lets people know if it’s safe to go based on bacteria levels.

Biologists aren’t always sure why bacteria counts spike. Sometimes it’s due to trash at candlestick park, or bird or dog feces.

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Walsh said San Francisco has a combined sewer system. “When it reaches capacity it’s designed to release into the Bay and the ocean with treatment that hasn’t received the full treatment that it would normally get at our plant. That [happens] sometimes during wet weather,” she said.