An Invisible Fall Phenomenon on Adirondack Lakes
by Mary Thill
Adirondackers have a dark fascination with deep water. This time of year, creatures that lurk near bottom in summer rise again to the surface. This phenomenon, known as autumn turnover, is happening now, invisible to most of us.
I know a fisherman who can tell when a lake has turned by the cloudiness of the water, but I need to see numbers. Last Saturday morning my husband, Mark, and I boated out on Lake Placid to take its temperature. The water was very clear, very placid. Mark lowered a sampling bottle. It sank out of view around 20 feet. At 30 feet, he shot an iron weight down the rope. The weight closed the lid and sealed deep water inside the jar as he pulled it back to the surface. He poured the sample into another bottle and I took its temperature: 50°F, about the same it’s been since June.
Mark repeated the process near the surface, collecting water about five feet deep: 57°F, much colder than the 68°F readings we got most of July and August. A water skier hooted like a loon as she dropped into the lake near the west shore. Still, as of Saturday, the top of the water was warmer than the bottom. Soon, maybe today, maybe tomorrow, the surface will cool to the temperature of the deeps, at which point the waters will mix, the lake will turn over.
Adirondack lakes of about 30 feet or deeper layer by temperature, starting in spring, as the sun warms the top, and denser, colder water is confined to deep basins. Lake trout, cisco, round whitefish and other fish that can’t tolerate 55°F or higher retreat downward. At turnover, they are freed to rise and spawn.
Back at the house, Mark stood at the kitchen counter filtering samples into smaller jars. He labels and mails them to a Department of Environmental Conservation lab in Syracuse, where they are checked for phosphorus, algae, pH, calcium and other indicators of lake health. Lake Placid is remarkably clear and well oxygenated. So far the depth, volume and flushing of its waters have offset fertilizers from lawns and septic-system leaks along its half-civilized, half-wild shore.
We sample the water every two weeks for the Citizen Statewide Lake Assessment Program, a partnership of the DEC and New York State Federation of Lake Associations. Surface ice on Adirondack lakes has been forming about two weeks later than it did in the 19th century, but no trend is yet evident in the timing of fall turnover in 110 lakes monitored through CSLAP. The long-term concern, as summerlike conditions extend into autumn, is that stratification might become prolonged, and deep-dwelling fish could run out of oxygen.