Algae are an important part of out freshwater and saltwater ecosystems. Too much algae growth, an algae bloom, can be a problem when it occurs in recreational waters. When the type of algae in a bloom can produce toxins these are called - harmful algae blooms.
Cyanobacteria, also known as blue-green algae, occurs in both salt and freshwater, but the blooms are of most concern in freshwater ponds and rivers. These blooms look like mats or thick paint on the surfaces of water. Blooms frequently appear blue or green but sometimes appear brown or red. These blooms can be harmful to people and animals. Contact with cyanobacteria can cause skin and eye irritation. Swallowing a small amount of water contaminated with cyanobacteria can cause gastrointestinal symptoms. Drinking large amounts may cause liver or neurological damage. Small children and pets are more susceptible to the effects of cyanobacteria than adults. Dogs, in particular, can get very ill and even die from ingesting cyanobacteria, either by directly ingesting it or licking it off their fur.