Swimming guides
The basics behind a safe swim
Short, sourced explainers on the two things that close a swimming spot, blue-green algae and fecal bacteria, plus the rain, rashes, and seasons that go with them. For the daily read on a specific water, check its state page or the nationwide map.
- Dogs
Blue-green algae and dogs
Cyanotoxins can kill a dog within an hour of a swim; here are the symptoms, the emergency steps, and how to keep it from happening.
Read the guide → - Field ID
What does blue-green algae look like?
Spilled paint, pea soup, and surface scum versus the harmless stringy algae, pollen, and duckweed people mistake for a bloom.
Read the guide → - Rain
Is it safe to swim after rain?
Why fecal bacteria spike for 24 to 72 hours after a downpour, and the roughly one-inch rain rule SwimZone uses to flag it.
Read the guide → - Rashes
Swimmer's itch, explained
The tiny bird parasite behind that shoreline rash, why it itches, how to treat it, and the towel trick that prevents it.
Read the guide → - Advisories
How beach closures actually work
E. coli in fresh water, enterococci at the coast, the 235 threshold, and why a posted advisory is often a day behind the water.
Read the guide → - Season
When is algae season?
Blooms peak in midsummer through early fall when water is warm, calm, and nutrient-rich, but the calendar shifts by region.
Read the guide →
These guides explain the hazards in general terms. They are not medical or veterinary advice, and they are no substitute for looking at the water and following posted signs. See how the daily verdict is built in the methodology.