Water Quality

by Clare Stevens, Water Quality/Environmental Committee Chairperson

I have been writing a series of articles based on the presentation made by our consulting limnologist, Dr. George Knoecklein, at the HLWA Annual Meeting last July. This article will explain changes that happen to our lake water and its chemistry during the summer season.

After “ice-out,” the sun warms the upper level of water to the depth its rays can penetrate. The warmer water becomes, the lighter it gets, and thus it floats on top of the colder water. The water depth where warm and cold water meet is called the thermocline; this area creates a boundary. By July, Highland Lake’s warm upper layer of water extends down about 15 feet from the surface. The water just below the thermocline mixes or turns over but can’t penetrate the upper level because it is too heavy. Thus, there is no exchange of dissolved oxygen and chemical materials.

The lower level of water, named the hypolimnion, continues to demand oxygen for decomposition of organic materials such as aquatic plants. Highland Lake has recently been going into the summer season with only 40% dissolved oxygen in the water below 25 feet as compared with 100% in 1935. As the summer progresses, there is 0% dissolved oxygen below 25 feet from the surface. The major impact of the lack of oxygen (anoxia) is it allows phosphorus to be released from the sediments in the lakebed. The danger is the phosphorus will reach the warmer, lighted water and feed an algae bloom.

The lack of oxygen also means fish are unable to survive in the water; they must migrate to a water level that contains sufficient oxygen. We are monitoring both oxygen supplies and water temperatures needed by the bass and trout population. It appears that by August, there is only a very narrow band of water that provides a vibrant habitat for these fish.

HLWA is discussing these aging trends with the DEP Water Bureau and Fisheries. As President Dick Labich mentioned in his message, we are also working to remedy the input of sand and silt through modifications at Sucker Brook Dam and researching alternatives to using sand and salt on the lake roads in the winter. In the meantime, please be aware our lake is “aging” and requires our maximum care. We appreciate the actions you take on your property to reduce the use of phosphates and erosion of silt and sand.

As summer commences and boaters are abundant, please remember Connecticut State Boating Regulations require you drive motorized vessels 100 feet from shore or docks if going more than 6 mph unless taking off or landing a water-skier. This regulation is not only for safety but helps reduce shoreline erosion and wave damage to docks and retaining walls. Personal watercraft must stay 200 feet from shore or docks.

If you have any questions, comments, or would like to help with water quality monitoring, please call me at 860.379.1596.

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