LIBERTY TOWNSHIP, N.J. (Warren County) — Tracking water quality in Mountain Lake has proven difficult this summer, as recent heavy storms and high temperatures have caused fluctuating algae levels and declining water clarity, the Mountain Lake Community Association reported Friday.
In a public update posted to its Facebook page, the association cited two storms on July 1 and July 14 — each delivering 2.5 inches of rain — as major contributors to recent water quality issues.
“The first storm involved more of a slow, steady rainfall, and did not result in any major, measurable impacts to the lake,” the post stated. A follow-up monitoring effort on July 9 found conditions “relatively stable and normal,” though a surface temperature of 86 degrees was recorded — “among the highest readings we’ve ever recorded.”
However, the July 14 storm brought intense rainfall and sediment-heavy runoff into the lake, particularly at the boat ramp and stormwater outfalls on the east side. Residents living near Mountain Lake Brook observed a significant surge of runoff entering the lake.
“Because phosphorus often attaches to sediment particles and is transported with them in runoff, the July 14 event essentially inoculated the lake with phosphorus, providing a heavy dose of ‘food’ for algae to feast on,” the update read.
Water testing on July 22 showed an increase in blue-green algae levels and a drop in clarity to 3 feet. Lab results received July 29 confirmed algae levels at 179,982 cells per milliliter. Toxin levels were not detected in the sample.
By July 30, conditions had started to improve, the group said.
“We found that the algae levels, as measured with our fluorometer, were less than they were a week prior. We also found that clarity had gradually improved, to 4.5 feet,” according to the post. “On the one hand, these findings indicate improving conditions. On the other hand, we recorded a surface temperature of 88 degrees, the highest we’ve ever recorded.”
The association noted the lake is resilient and rebounds when not subjected to major weather events. “The upshot is that Mountain Lake’s water quality is variable and tied to the weather. Intense rain storms and hot weather are not good for the lake, as reflected by downturns in water quality.”
The association remains in contact with the New Jersey Department of Environmental Protection and said it will share updates if the agency returns to sample for blue-green algae.
“Perhaps most important, we need to step up and do our best to protect the lake from water quality impacts,” the post concluded. “We are hopeful that the Township’s application for a grant to address the runoff problems at the boat ramp will be awarded — we should know by next month. And we urge everyone to support the MLCA in our efforts to implement the Lake and Watershed Restoration and Protection Plan developed earlier this year by Princeton Hydro.”
The next Mountain Lake Community Association meeting is scheduled for Sept. 11.
