Prospect Park visitors might see the cyanobacteria coming back in the lake due to warmer weather. 

Although the bacteria exists in low numbers, it can bloom during the summer months, appearing sometimes as if it was neon blue or green paint.

Certain types of the blue-green algae can produce toxins, and during bloom, can pose a health risk if ingested by either humans or animals. So officials are warning people to stay away from the water.

An official with the city’s Parks Department said the following: “Algae season is here, and when it is detected, we post signage around the lake to alert our park goers to keep them and their dogs safe. So, a reminder for dog owners—only take your pets swimming at the Dog Beach."

According to the state's Health Department, exposure to high levels of the algae can cause nausea, vomiting, irritation, breathing difficulties and more.