A quiet pond or slow-moving lake can look like the perfect place for a dog to cool off on a hot day. But in summer, some bodies of water develop harmful algal blooms, often caused by cyanobacteria, sometimes called blue-green algae. Some of these blooms produce toxins that can make dogs seriously ill, and exposure can be fatal.
Understanding the risk helps you decide when to let your dog in the water and when to keep them out.
When and where blooms happen
Harmful blooms tend to develop in warm, still or slow-moving fresh water that is rich in nutrients, such as runoff from fertilizers. Late summer is a common time, but blooms can appear whenever conditions are right. Ponds, lakes, reservoirs and slow sections of rivers can all be affected. Some blooms also occur in brackish water.
Dogs are especially vulnerable because they swim and play in the water, drink it and lick their fur afterward.
What a bloom may look like
Not every bloom looks the same, and you cannot always tell whether a bloom is toxic just by looking. Be cautious when water shows:
- Green, blue-green, brown or reddish discoloration.
- A scum, film or mat on the surface, sometimes resembling spilled paint or pea soup.
- Foam or clumps along the shoreline.
- A musty or unpleasant smell.
- Dead fish or other animals nearby.
Blooms can move with wind and currents, so water that looked clear one day may not be the next. When in doubt, keep your dog out.
Check advisories
Many state environmental and health agencies, as well as local parks, post advisories when harmful blooms are detected. Before visiting a lake or pond with your dog, check your state’s environmental or health agency website and look for signs at the water’s edge. Follow any posted warnings, even if the water looks fine to you.
Remember that the absence of a warning does not guarantee safety, since not every body of water is tested.
Signs of exposure and what to do
Symptoms can appear quickly, sometimes within minutes to hours after exposure, and may include vomiting, diarrhea, drooling, weakness, stumbling, difficulty breathing, tremors or seizures. Some toxins affect the liver and cause signs that develop more slowly.
If you think your dog has been in or drunk water that might contain a harmful bloom:
- Rinse your dog thoroughly with clean, fresh water, wearing gloves if you can, and do not let them lick their fur.
- Call your veterinarian or an emergency animal hospital right away, even if your dog seems fine.
- Tell them where your dog was swimming and what the water looked like.
The safest summer plan is simple: carry fresh drinking water, avoid questionable water and choose a kiddie pool, sprinkler or clean, well-maintained swimming area for cooling off.
