Why licking algae off fur isn't a lesser exposure
When a cat licks algae scum from their coat, they ingest a paste-like concentration of toxins, not diluted pond water. Their tongue's rough surface scrapes off more material than you'd expect—what looks like a 'tiny amount' to human eyes can be a lethal dose for a 4 kg cat. The diarrhea that follows isn't from bulk irritation but from direct toxin absorption through oral tissues.
Cats absorb certain algal toxins faster than dogs due to differences in mouth pH and enzyme activity. This means symptoms like diarrhea can appear within 30 minutes, faster than if they'd drunk the water. The rapid onset confirms significant toxin exposure, not incidental contact.
How grooming multiplies the danger
A cat who stepped in algae will repeatedly lick their paws over hours, creating ongoing toxin intake. Unlike a single drink, this staggered exposure overwhelms the liver's ability to detoxify incrementally. The resulting diarrhea may contain strands of algae visible to the naked eye—a clear exposure sign.
Paw licking also bypasses natural safeguards—when drinking, a cat might stop at the water's odd taste, but grooming is compulsive. They'll ingest toxins continuously until every trace is gone from their fur, potentially consuming more than if they'd taken one deliberate drink.
Why diarrhea means toxins are circulating
In blue-green algae poisoning, diarrhea occurs when toxins irritate the intestinal lining AND when the liver starts failing to process them. This dual mechanism means that by the time you see loose stool, the cat's body is already losing the battle on two fronts. The diarrhea may smell unusually sweet or pungent due to liver-derived toxins altering gut bacteria.
Unlike dietary diarrhea, this won't respond to fasting or kaolin treatments. The stool may have a greenish tint from bile pigments the liver can no longer recycle—an ominous sign that liver cells are dying faster than they can regenerate.
What to do before symptoms appear
If you saw your cat lick algae but no symptoms yet, don't wait. Toxins like microcystins have a 6-12 hour silent period before symptoms emerge—by then, irreversible liver damage may have started. Immediate vet care can administer binding agents to intercept some toxins still in the gut.
Bring photos of the algae and note the exact time of exposure. Time matters more than the apparent amount ingested—a pea-sized clump of scum contains enough concentrated toxin to kill a cat. Bathing the cat prevents further ingestion but doesn't remove absorbed toxins, so medical intervention remains urgent even after cleaning the fur.
The step-by-step response, from the first minute to the vet visit, is in our Blue-Green Algae / Cyanobacteria emergency guide.