Urban runoff may contain large amounts of bacteria from a variety of sources such as animal waste, soil, and decomposing vegetation. While many coastal storm drains within San Diego County are permanently posted with white metal warning signs, additional temporary warning signs are not posted for General Advisories. Activities such as swimming, surfing and diving should be avoided in all coastal waters for 72 hours following rain. This includes all coastal beaches and all of Mission Bay and San Diego Bay. Elevated bacteria levels can persist after a rainstorm depending upon the intensity of the storm, volume of runoff and ocean and current conditions.