By the time July heat has been sitting on Missouri for a few weeks, warm, slow-moving water — farm ponds, quiet lake coves, even backyard water features — can start growing something a lot more dangerous than it looks. Blue-green algae blooms are a real, recurring summer hazard for dogs in our area, and because so many of the dogs we groom are regular swimmers this time of year, we want every client to know what to watch for. Consider this a customer advisory: here's what blue-green algae is, why it's serious for dogs, and what to do if your dog has been in water that didn't look right.
This Isn't Hypothetical for St. Charles County
Blue-green algae isn't a distant problem. In 2024, the off-leash dog park pond at Broemmelsiek Park in St. Charles County closed for months after testing came back positive for cyanobacteria — the bacteria responsible for these blooms — at levels high enough to warrant closing the water to people and pets. The pond was eventually removed, and the county built a new dog park on donated land. It's one clear, local example of something that can show up in any warm, slow-moving water — a farm pond, a quiet cove on a lake, even a backyard water feature — not just the big, well-known lakes.
What Blue-Green Algae Actually Is
Despite the name, it isn't really algae — it's cyanobacteria, and it thrives in warm, nutrient-rich, slow-moving or stagnant water, which describes a lot of Missouri ponds and lake coves by the time July's heat has been sitting on them for a few weeks. A bloom usually looks like a thick paint-like scum or "pea soup" film on the surface, and it can be bright green, blue-green, white, red, or brownish. Foam along the shoreline and an unusual smell are other warning signs. The problem is that you can't tell by looking whether a particular bloom is producing toxins — some are, some aren't, and there's no visual way to be sure.
Why It's Genuinely Dangerous for Dogs
Dogs are at higher risk than people around this stuff for a few reasons: they drink a lot of water relative to their body weight, they'll swim and wade directly through a bloom, and afterward they groom themselves — so even a dog that never drank the water can ingest toxin by licking algae residue out of their own coat. According to veterinary sources including the American Animal Hospital Association and the ASPCA, cyanotoxins can cause liver failure or neurological symptoms, and signs can appear within minutes to a few hours of exposure. Reported symptoms include vomiting, diarrhea, drooling, weakness, pale or yellow gums, trouble breathing, tremors, and collapse. There's no antidote — it's a true emergency, not a wait-and-see situation.
Keeping Your Dog Safe This Summer
- When in doubt, stay out. Skip water that's discolored, has surface scum or foam, or smells off — and skip water with no posted information either way if you can't tell.
- Check for advisories before you go. Missouri's Department of Natural Resources keeps a statewide reports map of harmful algal blooms, and St. Charles County posts closures for county parks when testing turns something up.
- Don't let your dog drink from ponds or lakes — bring water from home instead, even on a hot day when a lake looks tempting.
- Rinse thoroughly with clean water right after any swim in a pond, lake, or river — not a chlorinated pool — before your dog has much chance to groom themselves. A prompt rinse at home matters more than anything a later appointment can do.
- Call your vet immediately if your dog shows any symptoms after being in natural water, even if you're not sure the water had a visible bloom. This isn't something to monitor overnight.
One thing worth saying plainly: grooming is not a safety net for algae exposure. If you have any reason to think your dog has been in a bloom, that's a call to your vet or an animal poison control line right away — not something to wait on until your next appointment. That said, if your dog's a regular swimmer this summer, a rinse-and-dry bath and brush between full grooms can help keep pond residue from sitting in the coat. Book an appointment here — we're at American Puppy in St. Charles.
Frequently Asked Questions
Is blue-green algae a real risk in St. Charles County, or just a national headline?
It's real and local. In 2024, the dog park pond at Broemmelsiek Park in St. Charles County closed for months after testing confirmed cyanobacteria at levels high enough to close the water. It can show up in any warm, slow-moving water, not just well-known lakes.
How can I tell if a pond or lake has toxic algae?
You can't always tell by looking, which is the tricky part. Warning signs include a thick paint-like scum on the surface, discoloration (bright green, blue-green, white, red, or brown), foam along the shore, or an unusual odor — but some toxic blooms don't look dramatically different from a normal pond. When you can't confirm the water is safe, the safest move is to skip it.
What are the symptoms of blue-green algae poisoning in dogs?
Vomiting, diarrhea, drooling, weakness, pale or yellow gums, trouble breathing, tremors, and collapse, often appearing within minutes to a few hours of exposure. This is an emergency — call your vet or an animal poison control line immediately rather than waiting to see if symptoms pass.
Can my dog get sick just from swimming, without drinking the water?
Yes. Dogs groom themselves after swimming, so licking algae residue out of their own coat can be enough to cause exposure, even if they never drank from the water directly.
What should I do right after my dog swims somewhere I'm not 100% sure about?
Rinse your dog thoroughly with clean water as soon as you can, before they have much chance to lick their coat, and keep an eye on them closely for the next few hours. If you notice any symptoms, or you have real reason to think the water had a bloom, call your vet right away rather than waiting.
Can a grooming appointment treat or rule out algae exposure?
No. Groomers can't diagnose or treat algae exposure — any concern about exposure or symptoms should go straight to your vet or an animal poison control line. A bath can help rinse residue out of the coat, but it's not a substitute for veterinary care, and it shouldn't delay a vet call if something seems wrong.