ROXBURY, NJ – Having decreased for a bit, the levels of potentially harmful bacteria in Lake Hopatcong appear to be increasing again, according to the state Department of Environmental Protection (DEP).

The DEP is using aerial sensing technology to detect the cyanobacteria involved in the ongoing “harmful algal bloom” (HAB) that prompted it last month to warn against coming into contact with the lake’s water.

Sensors on the aircraft “pick up wavelengths of light specific to the cyanobacteria pigment phycocyanin in a water body,” the DEP explained. This allows scientists to estimate the number of bacteria in HAB colonies.

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Aerial surveys that took place Wednesday showed an upswing in phycocyanin over the levels detected June 30, when the DEP said the intensity of the bloom appeared to be diminishing.

“Today’s flight (7/10/19) shows that the phycocyanin levels have increased over a large portion of the lake,” said the DEP late Wednesday.

Cell counts above 20,000 cells/mL prompt the state to issue advisories against coming into contact with water or allowing pets to go in the water. HABs can cause skin rashes and respiratory problems, according to the state. There have been reports of people ending up in emergency rooms after ignoring the state's warnings to stay out of the water.

Cyanobacteria in HABs can produce poisons called microsystins. High levels of these toxins can cause more serious ailments including liver damage..

Water samples taken on Tuesday continued to show that – while some bacterial blooms are increasing in size and some are diminishing – none of the lake water tested came close to having dangerous levels of the microsystins.

The states’ health advisory level for microsystins is 3 ug/l. The highest level found on Tuesday was 1.45 ug/l. That was in a sample in the middle of the lake east of Davis Cove, said the DEP It was an area that did not have a particularly high concentration of bacteria, according to the samples.

However, the Tuesday samples showed cyanobacteria cell counts as high as 79,000 cells/mL in Crescent Cove, River Styx. That’s about double the cells detected there four days earlier.

On the other hand, water samples at Prospect Point, which had 37,000 cells/mL on July 5, found only 6,000 cells on Tuesday, according to the DEP.

“Due to the characteristics of the lake, as the bloom progresses, some areas may test higher on some days than previous days," the state explained. "This variability is expected due to the shift in cyanobacteria populations, wind or water currents moving the blooms around the lake ... Results from sampling conducted on 7/9/19 show continued cell counts above advisory levels for both some recreational bathing beaches as well as some open water lake locations,” said the state.

Lake Hopatcong's bloom is the largest, but the lake is not the only water body in New Jersey experiencing an HAB. According to the DEP there are continuing HABs in Lake Mohawk, Spruce Run Reservoir and several other lakes. is a member of the New Jersey Press Association and is a hyperlocal news site that serves residents, organizations and business owners of Denville, New Jersey.

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