Blue-Green Algae and Dogs
Dogs are the most common victims of blue-green algae poisoning. They wade into scummy shallows, drink lake water, and lick it off their fur, so they take in far more toxin than a person would. A toxic bloom can kill a healthy dog within hours, and there is no antidote, only supportive veterinary care. If you think your dog has been in water with blue-green algae, treat it as an emergency and call a veterinarian right away.
Why dogs are especially at risk
- They drink directly from the lake, swallowing concentrated toxin.
- They swim through and wade into the downwind shallows where scum piles up.
- They lick their fur afterward, ingesting even more.
- They can’t tell you they feel sick until symptoms are advanced.
The toxins
Blue-green algae are cyanobacteria, and some strains produce potent toxins. Two matter most for dogs:
- Anatoxin-a is a fast-acting neurotoxin. It can cause tremors, seizures, and respiratory paralysis within minutes, which is why it was once nicknamed “very fast death factor.”
- Microcystins are liver toxins. They cause vomiting, diarrhea, and progressive liver failure over hours to a few days.
You cannot tell whether a bloom is toxic by looking at it, and the same lake can be safe one week and dangerous the next. Treat every visible bloom as potentially poisonous.
Symptoms of blue-green algae poisoning in dogs
Symptoms depend on the toxin and can come on fast. Watch for:
- Neurologic (anatoxin): excessive drooling, muscle tremors, weakness or stumbling, seizures, difficulty breathing, blue gums, collapse.
- Liver (microcystin): vomiting, diarrhea (sometimes bloody), lethargy, loss of appetite, pale or yellow gums, disorientation.
Because anatoxin can act within 15 to 60 minutes, do not wait to see whether symptoms develop.
What to do if your dog was exposed
- Get to a vet immediately, even if your dog seems fine. Call ahead so the clinic can prepare, or go straight to an emergency animal hospital.
- Rinse your dog thoroughly with clean, fresh water.
- Stop them from licking their fur so they don’t swallow more toxin.
- The ASPCA Animal Poison Control Center (888-426-4435) can advise while you travel.
There is no specific antidote for cyanobacteria toxins, so early supportive care, and speed, give your dog the best chance.
Check a lake before you go
The safest habit is to check conditions before your dog gets near the water. Look for these warning signs at the shoreline: water like spilled green paint or pea soup, thick surface scum, bright green streaks, or a musty, sewage-like odor. Then use the data:
- On any lake’s LakeQuality page, check its algae (chlorophyll-a) level and, where available, its satellite blue-green algae reading from EPA CyAN.
- Read our blue-green algae guide for how blooms form and which lakes are most prone to them.
- Check your state health or environmental agency for the current bloom advisory, blooms can change within days.
Bloom-prone lakes to be cautious around
These lakes carry the highest chlorophyll-a (algae) levels of every lake LakeQuality tracks, a sign of chronic, nutrient-driven bloom risk. High algae doesn’t guarantee toxins, but these are waters to check carefully before letting a dog in.
| Lake | County | State | Algae (µg/L) | Grade |
|---|---|---|---|---|
| Lake Wooldridge | Saline | MO | 777.8 µg/L | F |
| Pomme de Terre Lake | Hickory | MO | 360.5 µg/L | F |
| Bee Tree Lake | St. Louis | MO | 296.4 µg/L | F |
| Buffalo Lake | Pierce | ND | 219.5 µg/L | F |
| Knox Village Lake | Jackson | MO | 193.5 µg/L | F |
| Mckay Park Lake | Cole | MO | 187.1 µg/L | F |
| Ardmore Lake | Hennepin | MN | 185 µg/L | F |
| Crowder S.P. Lake | Grundy | MO | 176.4 µg/L | F |
| Limpp Lake | Gentry | MO | 166.5 µg/L | F |
| Loose Park Lake | Jackson | MO | 159.8 µg/L | F |
| Juanita Lake | Foster | ND | 154.2 µg/L | F |
| Drexel City Reservoir South Nr. Dam | Bates | MO | 152.7 µg/L | F |
| Lewis Lake | Stoddard | MO | 149.8 µg/L | F |
| Quiver Lake | Mason | IL | 140 µg/L | F |
| Boujan Swale Lake | Cass | IL | 136 µg/L | F |
Prevention checklist
- Skip any water with visible scum, discoloration, or a posted advisory, no exceptions.
- Bring fresh drinking water so your dog isn’t tempted to drink from the lake.
- Rinse your dog with clean water after any swim, and dry them off.
- Be most cautious in warm, calm weather from July through September, when blooms peak.
- Favor deep, clear, well-graded lakes over shallow, warm, high-nutrient ones.
Frequently Asked Questions
Can blue-green algae kill a dog?
Yes. Some blue-green algae (cyanobacteria) produce toxins that can be fatal to dogs within minutes to hours of exposure. The neurotoxin anatoxin-a can cause respiratory failure very quickly, and the liver toxin microcystin can cause fatal liver damage over hours to days. There is no antidote, so speed of veterinary care is critical.
How quickly do symptoms of blue-green algae poisoning appear in dogs?
Neurotoxic symptoms (drooling, tremors, weakness, difficulty breathing, collapse) can begin within 15 to 60 minutes. Liver-toxin symptoms (vomiting, diarrhea, weakness, pale gums) may take a few hours to a day. Because onset can be rapid, do not wait for symptoms if you know your dog was in scummy water — go to a veterinarian immediately.
What does blue-green algae look like?
Blue-green algae often looks like spilled green or blue-green paint, pea soup, or a thick surface scum, sometimes with a musty or sewage-like smell. It can collect along downwind shorelines where dogs wade. But toxic blooms are not always obvious, so a lake that looks clear can still be unsafe.
What should I do if my dog drank lake water or swam in a bloom?
Treat it as an emergency. Rinse your dog thoroughly with clean water and prevent them from licking their fur (they can ingest more toxin while grooming). Then contact your veterinarian or the nearest emergency animal hospital right away, even if your dog seems fine. The ASPCA Animal Poison Control Center (888-426-4435) can also advise.
Is it safe for my dog to swim in the lake?
Avoid any water with visible scum, discoloration, or a posted advisory. Blue-green algae is most common in warm, nutrient-rich (eutrophic) lakes in mid-to-late summer. Check the lake’s page on LakeQuality for its algae levels and satellite bloom status, and check your state health or environmental agency for current advisories before letting your dog in.
This guide is general safety information, not veterinary advice. If you suspect blue-green algae exposure, contact a veterinarian immediately. Authoritative sources: American Kennel Club, ASPCA, and EPA HABs.