San Diego Water Quality & Beach Advisories

Most closures fall into three buckets: confirmed sewage contamination (a spill or cross-border flow), bacterial exceedance following rain, or a public-safety hazard (shark sighting, water rescue, hazardous debris). The first two come from the county Department of Environmental Health; the third comes from city lifeguards and can lift within hours.

Areas that close most frequently: Imperial Beach, Silver Strand State Beach, the south end of Coronado, and Border Field State Park during wet months. Areas that close almost never: La Jolla Shores, Del Mar, the North County beaches from Cardiff to Oceanside.

The Tijuana River drains a large urban watershed in Mexico that lacks the wastewater capacity to handle storm flows and aging-infrastructure spills. The result: millions of gallons of untreated sewage flow north across the border each year, enter the ocean near Imperial Beach, and drift up the coast on prevailing currents. It's the single largest reason Imperial Beach holds the worst water-quality record in California.

Federal funding for upgrades to the South Bay International Wastewater Treatment Plant is moving forward, but completion is years out. Until then, Imperial Beach and the south end of Coronado will see frequent closures, especially in winter.

The giant-kelp forest off La Jolla is one of San Diego's signature underwater ecosystems — and it has been thinning for decades, mostly because purple urchins (no longer controlled by sea otters along this stretch of coast) overgraze young kelp. Restoration divers from The Bay Foundation, Sundiver, and local volunteer dive teams cull urchins in targeted plots, letting kelp recolonize. Sections of the cove are noticeably greener than five years ago.

Surfrider San Diego and San Diego Coastkeeper organize monthly shoreline cleanups that anyone can join — the easiest way to plug in if you don't dive.