New York State Parks announced that Lake Welch Beach in Rockland County reopened Tuesday. It comes after a harmful algal bloom was found last week and treated.

News 12 saw many people at the lake Tuesday afternoon, either soaking up the sun or taking a dip to cool off from the hot temperatures.

"We saw that these couple of days are going to be 100 degrees, 90s – so we thought why not come over here,” said Sean Palacios, of New Jersey. "It's great to be back here. Finally."

Harmful algal bloom, or HAB, can cause health problems for humans and animals. Since HAB was spotted last week, New York State Parks says the water was treated with algaecide. Then, when the water looked clear, it was tested and shown to be safe for swimming.

"We're on top of things and that we're monitoring every day. We have staff that's out here very early in the morning,” Ed McGowan, an environmental stewardship told News 12 Tuesday.

The lake has buoys that keep an eye on HAB. McGowan said, "As these pigments increase, it's not something that we can see with our eyes, but the monitoring device can pick up. And let us know it's coming. They also have ultrasound that is meant to kill the HAB's around them, but that's more experimental at this stage."

Lake Welch Beach was closed for much of the summer 2022 season because of HAB. Meanwhile, some Putnam county beaches remain closed to harmful algal bloom.