In the Fall and Winter, the lake drain valve is opened in order to lower the lake level, thus minimizing shoreline erosion due to ice movement during the Spring thaw. Depending on weather conditions, the drain valve is closed in the late Winter or early Spring to refill the lake. If the lake and/or the ground isn't frozen, and/or there is no snow on the ground, typically the drain valve is closed in January. If there's a foot or so of snow on the ground and the lake is frozen, closing the valve can wait until mid to late February, or even later. It has been closed as early as January and as late as April. In both of those extreme cases, the lake has been full again before the start of Summer.
In more detail, this is how the decision to close the valve is made. In the Spring, the average air temperature usually, but not always, starts to go above freezing in early to mid March. This starts refilling the lake from the thawing watershed, as well as melting the lake ice. The SAME water running off the watershed both refills the lake and melts the ice. UNTIL THIS HAPPENS, CLOSING THE DRAIN VALVE HAS LITTLE EFFECT ON REFILLING THE LAKE. The trick is to decide how much ice melting is needed to minimize shoreline erosion before the valve can safely be closed, to actually refill the lake. If it is closed too soon, the water level gets too high and the ice has more opportunity to cause damage. If done too late, the water that could be used to refill the lake is released, making it difficult to get the lake full by May 15th. The difference between "too soon" and "too late" can be as little as a week; but usually not.
Since the weather station has been installed, the decision to close the drain valve is based on the 10 day weather forecast for our area, on Weather Underground, that predicts average temperature above freezing for several days and maybe even beyond.(The 10 day forecast is available when you access our weather station on line. It is because of all the small weather stations like our own, that 10 day weather forecasts are even possible.)
Also, the DEC permitted weed treatment, which usually occurs in May, requires that no water be released from the lake for two weeks. This generally means keeping the lake level lower than ideal in May. Unfortunately, this is also about the time when lake users want the lake full. The only thing to be done at that point is to hope that it rains an inch or so after the weed treatment, but before Memorial Day. This is why in some years it can take until June to get the lake full.
While the maximum amount the lake can be lowered is about 24 inches, the downdraw has been limited to about 18 inches since 2002, because the lake was not getting full enough in some prior years.
With the exception of the extremely dry year of 2012, since 2002 the lake has consistently been raised to the spillway every Spring. However, once the level is at the spillway, Nature controls what happens to the level from then on. That is, especially in the Summer, the lake level is ALWAYS going down, unless it is raining.
To view a more detailed presentation on Lake Level in pdf format, complete with maps, photos, and data, click here