WEST MILFORD, N.J. (CBSNewYork) – Swimming is banned at another New Jersey lake because a harmful algae.

State officials are warning to not even touch the water, reports CBS2’s Vanessa Murdock.

First warnings were posted at Lake Hopatcong a few weeks ago. Now swimmers are being warned to stay out of Greenwood Lake.

While the hottest days of summer force involuntary sweating, a dip in Greenwood Lake would be awfully refreshing, if it were safe to do so.

Picturesque Greenwood Lake is being plagued by word from the DEP that harmful algae is blooming.

Typically people flock to the lake to cool off in the fresh water, but now globs of green mar the surface of this New Jersey gem.

“What would this lake normally look like? Crowded,” said Dennis Vandunk of Franklin.

For now, it’s empty. An impossible-to-miss red sign warns of danger from a harmful algae bloom. Neither humans nor animals should come into contact with the water – even fish caught there shouldn’t be eaten.

“It was just a stunning place to be,” said Liz Derose, who lives in Mahwah now but grew up on the lake and used to swim in the water all the time. “It was spotless. You could see the bottom, it was gorgeous.”

She says to know you can’t swim in the lake now is a huge disappointment.

“It really is a horrible thing, but we’re the cause,” she said. “It’s about the chemical the fertilizers it’s about sewage running into the lake.”

MORE: Town Of West Milford Harmful Algae Warning Notice

Blooms are typically caused by cyanobacteria in run-off, and on hot days help the potentially toxic algae to blossom.

Ingesting this water could cause vomiting, nausea and blistering around the mouth, and if you touch the algae, you may get a skin rash.

Algae bloom as of June 27, 2019, on Lake Hopatcong in New Jersey. (credit: CBS2)

MORE: Algae Bloom Spoils Swimming In New Jersey’s Lake Hopatcong For Weeks

“I have a friend that lives over here, he is upset… they were supposed to have a party… everybody waterskiing. Can’t do it,” said Dennis VanDunk of Franklin.

“Heavy rain is washing nitrates and phosphates into the lake and we are fertilizing this bacteria,” said Dr. Angela Cristini, professor of biology at Ramapo College.

Add heat to warm the water and you’ve got problems.

“Get it on your skin, it can cause skin lesions or blisters. It can cause distress on your eyes. Swallow it and it will cause distress for sure,” Cristini said.

Ingesting the water could cause vomiting, nausea.

The warning means little to 15-year-old Frankie Toscano, who told Murdock he wouldn’t miss the opportunity to zip around on his personal water craft.

“There’s a little fear factor but I’m not going to let it stop me,” he said. “My mom’s on the fence, my dad’s whatever, go do it.”

It’s imperative to note two things: The DEP says boating is completely safe on the lake. Second, swimming is safe on the New York side: No harmful algae was found there.

This isn’t the first New Jersey lake to be closed off to swimmers. Drone Force 2 flew over Lake Hopatcong about three weeks ago when we first got word of the DEP posting the same warning on the largest lake in the Garden State.

CBS2’s Cindy Hsu spoke with residents there back on June 28.

“It was green, it was thick, it was almost like someone poured oil paint on top of the lake,” said Hopatcong resident Robin Delorenzo. “The smell was almost rotten egg like.”