HOPATCONG, N.J. (CBSNewYork) – A warning for swimmers in New Jersey: Stay out of a popular lake, or you could get sick.

Chopper2 was over Lake Hopatcong this afternoon where officials say a harmful algae bloom has formed in the water.

Contact with the water can lead to a range of health issues, from rashes to flu-like symptoms.

Often referred to as blue-green algae, cyanobacteria are not true algae but are capable of excessive growth through photosynthesis. Cyanobacteria blooms are usually a bright green, but can also appear as spilled paint, “pea soup,” or as having a thick coating or “mat” on the surface. These blooms can often be confused for typical algae blooms

Heavy rainfall and storm-water, followed by warm weather are to blame.

Officials say the bloom could stick around for weeks.