Don't swim or even touch the water in Lake Hopatcong, state officials advised Thursday.

The New Jersey Department of Environmental Protection issued the advisory after it confirmed the presence of an extensive harmful algal bloom through aerial surveillance.

Lake conditions threaten Fourth of July holiday vacation plans for thousands and peak season revenue for hundreds of businesses related to the lake, a major economic driver for four border towns in two counties.

"Based on the widespread nature of the HAB, the recreational advisory may be in place for weeks, if not longer," DEP officials advised. "The duration is unpredictable and may be influenced by availability of nutrients and weather conditions." In 2018, harmful algal bloom was observed on water bodies well into the fall season, according to DEP.

Exposure to the algae can cause health problems such as rashes, allergy-like reactions, flu-like symptoms, gastroenteritis, respiratory irritation, skin rashes and eye irritation.

The rapid spread may be the result of heavy rainfall that carried nutrient-laden stormwater into the lake, followed by periods of warm weather, DEP officials said.

"While this current situation appears to be a product of Mother Nature, it could not have happened at a worse time for recreation and businesses around the lake as we head toward the holiday weekend," said Assemblyman Anthony Bucco, who represents bordering lake towns in the 25th District.

DEP issued an advisory on Friday, warning the public of harmful algae growth reported on June 17 by residents in the area of Pebble Beach and Sand Harbor Beach. Those beaches were closed by the Sussex County Health Department.

Since then, additional harmful algal bloom sightings have been reported in the Byram Bay, Crescent Cove and River Styx areas, mostly from residents and private marinas.

Residents in those areas were advised to avoid contact in waters where the algal growth was suspected, to not eat fish caught there and prevent pets and livestock from water contact as well.

Mount Arlington Beach was closed for the same reason Monday, but was reopened Tuesday.

"Our No. 1 priority must be to protect the public, and right now, Lake Hopatcong could be dangerous," said Sen. Joseph, Pennacchio, who represents Jefferson on the eastern shore in the 26th District. "I fully support the NJ DEP’s decision. There is no other choice."

Jeff Tittel, director of the New Jersey Sierra Club, cast blame for the lake condition on the failure of the Gov. Phil Murphy administration for failure "to reverse eight years of rollbacks on waterways that have led to increased pollution and overdevelopment.

“This is what happens when we eliminate environmental protections and don’t protect our waterways," Tittel said "We fail to control overdevelopment, failing septics and stormwater. Warmer temperatures and more rain means more runoff from overdevelopment and farms. That brings more nutrients and silts creating a witches’ brew in our lakes. Climate change will worsen those impacts."

Tourist dollars

The largest body of freshwater in New Jersey, Lake Hopatcong developed a thriving tourist trade before the turn of the 20th century, luring wealthy New Yorkers to luxury lakefront hotels and delivering them via direct railroad.

More than a century later, most of the lake, which covers 4square miles, is now mostly bordered by permanent residences and a large variety of businesses, from boat rentals, marinas and bait shops to restaurants and nightclubs.

“Lake Hopatcong drives our local economy and generates tourism and economic revenue for the entire state," said Sen. Anthony Bucco (R-25). It’s a beloved destination for families throughout the country. The NJ DEP’s recommendation is the right call, and we will do everything we can to restore safety conditions as soon as possible.”

Lake Hopatcong State Park was closed for two days last August when high levels of E.coli bacteria were detected after an extended period of rain.

One man who rented a boat for his birthday last month drowned after diving off his rental into a shallow area, where witnesses said he became entangled with bottom weeds.

"We usually don’t see HABs like this until August. Now we’ve got two lakes already closing in June,” said Tittel. "We’re creating a vicious cycle that will only bring higher temperatures, more rain and more pollution. More beaches and swimming areas will close."

“I know that there will be a number of families, near and far, who will be heartbroken by the decision to close public beach access to the lake, especially given the time of year,” said Senator Steven Oroho whose 24th District includes Hopatcong borough, which sits along the lake's western shoreline in Sussex County. “That being said, the state has a responsibility to keep people safe from harm. We can’t ignore these high levels of toxic algae. I urge local residents and tourists to follow the DEP’s recommendation to avoid all contact with the water.”

New trainee:Seeing Eye dog missing; $500 reward 'no questions asked'

Terrifying journey:'Miracle' kitten hitches ride across NJ by clinging to tractor-trailer's undercarriage

William Westhoven: 973-917-9242; wwesthoven@dailyrecord.com.