There are already several cases of dogs poisoned by bathing (ingesting) in waters of some lakes in the United States. The reason for this is toxic blue-green algae (sometimes algae look like grains of sand or floating green foam). Threats to animal health range from skin rashes to neurological problems.
This has led to a ban on swimming from lakes in the Pacific Northwest to the entire Mississippi coast, to Hopatcong Lake, the largest lake in New Jersey. Cyanobacteria, the main organisms that produce toxins that harm freshwater blooms, can cause ailments in people, but dogs are more susceptible because they ingest them.
Algae blooms tend to thrive at high temperatures and after heavy rains carry fertilizer runoff and sewage to the waterways. Thus, blooms can release toxins that can cause liver damage, cause respiratory paralysis or produce other fatal conditions.
These algae are particularly dangerous for dogs because, while the sight and smell of algae repel humans, animals sometimes lick the water, ingest floating pieces of algae or throw themselves on them. Toxic algae can also be crusted on the mainland, where dogs can nibble on them. Some of these infected dogs, in fact, have a fatal prognosis, because there is no cure for poisoning, and exposure almost always leads to death.
Blue-green algae are more common in the summer. Toxic algal blooms are more likely to infect freshwater bodies when the weather is warm and the waters are stagnant, according to the North Carolina Department of Health and Human Services. As general advice, lor better for humans and pets is to avoid water that smells bad or looks strange or cloudy.