That cloud of pea soup floating on your favorite watering hole could be more than just messy slime. It might be chock full of toxins that can be life-threatening to your dog or cat.

Blue-green algae, also known as cyanobacteria [sigh-a-no-bacteria], is actually a group of bacteria that can also be poisonous to horses, birds and cattle drinking from the water source. Clouds of the stuff can bloom almost overnight when water levels are low, particularly in the dog days of summer. Blue-green algae thrives in areas of nutrient run-off, like water surrounded by recently fertilized land that’s exposed to heavy rains. Ingestion of even small amounts of certain types of blue-green algae can be fatal in just minutes to hours.

So if your furry friend wants to swim in or drink from a slime-covered pond, take a rain check. Don’t risk the consequences with this menacing mess.