A growing global problem, harmful algal blooms are not caused by true algae but rather by cyanobacteria that in many ways resemble and behave like algae. These cyanobacteria naturally occur in fresh water and can proliferate to unhealthful levels in sunlight and hot weather, forming dense mats resembling pea soup or spilled paint.
Exposure to cyanobacteria cells can cause a range of mild to moderate health effects, including rashes, allergy-like reactions, flu-like symptoms, gastroenteritis, respiratory irritation and eye irritation. Incidental ingestion of water containing the toxins these bacteria can produce, known as cyanotoxins, can result in more serious health effects such as liver toxicity and neurological effects. Children and pets are more vulnerable because they ingest more water in relation to their weight.
More information- https://www.state.nj.us/dep/hab/