Is it safe to swim after it rains in San Diego?
No. San Diego County advises staying out of the ocean and bays for 72 hours after rain stops. The trigger is a fifth of an inch, and no warning signs go up for it — the beach will look completely normal.
- Wait after rain
- 72 hours
- Advisory trigger
- 0.20 inch of rain
- Signage
- None for rain advisories
- Keep away from outfalls
- 75 feet minimum
From when the rain stops
Coastal or valley areas
Bacterial advisories do get signs
Storm drains and creek mouths
The short version
- The county issues a general rain advisory whenever coastal or valley areas get 0.20 inch of rain or more.
- It runs for 72 hours after the rain ends — not 72 hours after it started.
- No signs are posted for a rain advisory. A beach under one looks exactly like a beach that isn't.
- Storm drains and creek outlets are the worst of it: stay at least 75 feet from where runoff enters the water, any time of year.
- Bacterial advisories are a different thing and do get white warning signs.
San Diego rains rarely and then all at once, onto a city built of hard surfaces that drain straight into the ocean. Everything on the streets for the previous dry month goes with it. That is why the county's advice after rain is not "be careful" but stay out of the water.
When the clock actually starts
The most common way people get this wrong is counting from the start of the storm. A wet Friday night means Monday night, not Monday morning.
Why rain specifically
Urban runoff carries bacteria into coastal water at levels that routinely exceed state health standards, and the concentration is highest near the places the runoff arrives — storm drains, creek mouths, lagoon outlets. The county's Beach and Bay Monitoring Program samples the water, but sampling and lab results take time; the blanket 72-hour advisory exists precisely because the risk is predictable even before anyone has tested anything.
The four things the county actually issues
| Type | What triggers it | Signs posted? |
|---|---|---|
| General rain advisory | 0.20 inch of rain or more; lasts 72 hours after rain ends | No |
| Bacterial exceedance advisory | Lab testing shows water fails state health standards | Yes — white advisory signs |
| Precautionary advisory | Dredging or excavation near a lagoon or river outlet | Yes — white signs |
| Outfall warning | Permanent, at storm drains and creek outlets | Yes — white signs at the outlet |
Source: San Diego County Department of Environmental Health and Quality, Beach and Bay Monitoring Program.
Surfers are the group this hits hardest, because a storm is often when the waves arrive. It is a real trade-off rather than an imaginary one, and it is worth making deliberately rather than by not knowing.
Rain is concentrated enough here that this affects a small number of days: December through March is effectively the whole wet season. If you are visiting between May and September the question barely comes up.
KEEP READING
SOURCES
Everything above traces back to one of these. Follow them — if one has changed and we haven't, that's our mistake, not yours.
San Diego County Department of Environmental Health and Quality · Checked September 8, 2026
The 0.20-inch trigger, the 72-hours-after-rain-ends rule, the absence of signage for rain advisories, the other advisory types, and the 75-foot outfall guidance.
San Diego County Land and Water Quality Division · Checked September 8, 2026
How the county samples and what the standards are.
Times of San Diego · December 24, 2025
A recent example of the advisory being issued in practice.