Why is water at SLO County beaches unsafe after a storm? Health advisory explained
After the first atmospheric river-fueled storm of 2025 swept through San Luis Obispo County, health officials told residents to avoid the ocean.
Locations across the county received anywhere from a 0.07 of an inch to more than 4 inches of rain, according to the San Luis Obispo County Department of Public Works.
On Tuesday, the San Luis Obispo County Public Health Department issued a rain advisory warning swimmers, surfers and others to stay out of the water for at least three days — especially in areas “close to creeks, rivers, storm drains and other runoff outlets that empty into the ocean,” according to a news release.
Why is it dangerous to wade in the surf after a storm? And when will it be safe to enter the waves again?
Here’s what public health officials say:
Why does SLO County issue public health advisories?
Public health advisories are usually issued following “significant rain events” where heightened levels of bacteria are expected in storm water runoff, the SLO County Public Health Department said on its website.
A significant rain event is defined as at least half an inch of rain accumulated over a 12-hour period, said Jeremiah Damery, a supervising environmental health specialist for SLO County.
Why is it dangerous to swim after a storm?
Storm water run-off is full of dangerous bacteria that can cause serious health issues, the Public Health Department said.
In a Tuesday news release, the agency said that rainstorm runoff “is known to transport high levels of disease-causing organisms such as bacteria, viruses and protozoa from the watershed and urban areas to the ocean.”
Ingesting these organisms could cause skin, respiratory and intestinal problems, health officials said.
Children, older adults and people with compromised immune systems are especially vulnerable to waterborne pathogens.
The bacteria could cause eye, ear, nose and throat infections, Damery said.
Is it safe to walk on the beach during a rain advisory?
Walking barefoot on the sand after a storm is not dangerous to your health, Damery said.
The real health risk is if you come in contact with ocean water close to where rivers, streams, creeks or storm drains empty into the ocean, he said. These sites typically have a concentrated amount of bacteria.
“I wouldn’t let my kids play in the water right where the dirty creek is washing out, especially after a storm,” Damery said.
How long should you stay out of the water?
After a rain advisory is issued, public health officials urge people to avoid water contact for 72 hours following an intense storm.
However, Damery told The Tribune, an advisory could stay in place longer than three days if a prolonged storm occurs or if major rain events occur in the same week.
For the latest information on beach water quality in SLO County, visit SurfSafeSLO.org or call the Ocean Water Monitoring Program Telephone Hotline at 805-788-3411.
This story was originally published February 5, 2025 at 3:54 PM.
