Spring 2023 Issue

Water Quality Report
Doesn’t Mince Words:
Lake is Getting Hotter
12
Story by MICHAEL DAIGLE
Photos by KAREN FUCITO
The work needed to clean up Lake
Hopatcong is being done in many ways,
both in the lake and offshore.
Lake weeds are being cut and harvested. Better
filtration is being used to clean runoff before it
gets to the lake. Chemical treatments are being
used to combat outbreaks of heavy pollutants.
Pollution-absorbing shoreside wetlands are
being restored and floating in-lake wetlands are
being planned and installed.
Even bigger projects—sewers and channel
dredging—are being planned, pending funding.
There are even projects of a smaller scope:
Efforts to discourage Canada geese from settling
in and raising families are ongoing, and the
measurement of the influx of microplastics and
salt have begun.
Progress, all.
But none of these efforts directly address an
underlying concern: New Jersey’s largest lake is a
2,600-acre pot of slowly boiling water.
“There has been a statistically significant
increase in surface water temperatures at Lake
Hopatcong over the past 33 years,” stated the
2022 Lake Hopatcong Water Quality Report,
issued in December by the consulting firm
Princeton Hydro LLC.
“It should be noted that each year from 2019 to
2022 were in the top six of the highest recorded
July surface water temperatures dating back to
1988,” the report said. “The highest surface water
July temperature at Station 2 [mid-lake between
River Styx and Van Every Cove] was recorded in
2005 and was 28.5 degrees Celsius [83.3 degrees
Fahrenheit].”
On it goes: “The July 2022 surface water
temperature at Station 2 was the fourth highest
recorded at 27.5 degrees Celsius [81.5 degrees
Fahrenheit.] These data provide evidence that
climatic change is impacting Lake Hopatcong.
In turn, increasing water temperatures make the
lake more favorable for larger and more frequent
harmful algal blooms (HABs).”
The 2022 report signified an important shift in
the collection and analysis of the data.
“This analysis was conducted to assess the
potential impacts of climate change on Lake
Hopatcong. The Station 2, mid-lake data were
used because there was no chance of shading
from near-shore trees or structures at this
location.”
Fred Lubnow, director of aquatic programs
for Princeton Hydro, said the continually rising
temperature of the lake’s water influences a
LAKE HOPATCONG NEWS Spring 2023
variety of results.
Trout, for example,
thrive in cooler water.
A three-year study is
being conducted jointly
by the Lake Hopatcong
Commission, Lake
Hopatcong Foundation
and Knee Deep Club
to determine how
many trout stocked in
the spring each year survive the higher water
temperatures of the summer.
Last year, anglers reported they caught 16 of
the 1,000 specially tagged brown trout that had
been stocked in April, the club said.
These trout are in addition to the roughly
9,000 trout released in Lake Hopatcong
annually by the New Jersey Division of Fish and
Wildlife.
Club member Tim Clancy attributed the low
number of caught tagged fish reported last
year to lack of information about the special
program. He said the club is redoubling efforts
this year to educate the fishing community
about the project. For more information visit
kneedeepclub.org.
The 2022 water quality report indicates the
rising temperature of the lake was a factor in the
dynamic conditions affecting trout habitat.
“Optimal habitat” for brown trout, the highest
standard, is defined as waters with dissolved
oxygen concentrations equal to or greater than
5 mg/L and water temperatures less than 65
degrees.
“Acceptable or carry-over habitat,” a lesser
standard, is defined as waters containing
dissolved oxygen concentrations equal to or
greater than 5 mg/L and water temperatures
up to 79 degrees. Those are conditions in which
trout may be able to “carry over” or survive the
warmer summer water temperatures until the
lake cools in the fall.
The existence of trout habitat varied greatly
from month-to-month last year, the report said.
Examples: On July 11, there was carry-over
habitat present in the upper 15.3 feet of Station
2. On July 18, the available habitat had been
squeezed to a width of 1.5 feet between depths
of 12 and 13.2 feet. The report indicates that was
a dramatic change.
In May and June both optimal and carry-over
habitats were measured between 20 feet and 68
feet.
But, the report said, “sampling conducted
on July 5 as part of the trout study revealed
extremely limited optimal brown trout habitat
One of a thousand specially tagged trout released into Lake Hopatcong
last year.
throughout the lake as a result of increasing
temperatures…as well as the anoxic (oxygen
deficient) conditions creeping upwards in the
water column.”
On October 6, with cooler water, the optimal
trout habitat was present in the upper 38.43 feet
of the lake.
In a video presentation to the Lake Hopatcong
Foundation on the 2022 report, Lubnow said
studies are suggesting another heat-related
issue: As the lake warms, the chemical bond in
the lake sediment between iron and phosphorus
is breaking, releasing more phosphorus into the
lake water.