Lake residents were excited to see the ice melt off the lake with boaters and kayakers out early, smashing through the ice to break it away.  The Official ice-out date was March 26 this year.

Lakes freezing plays a critical role in our environment. A lot of life continues during the winter, including rooted plant green algae, blue-green algae (cyanobacteria) bacteria, and fish growth goes on during winter.  The lake does not sleep during the winter.

Water exists as a solid, liquid, and gas, which makes it unique. Water density changes with temperature and water are less dense as a solid at 0 °C (32°F) than when it is at a temperature above and below 4.0° C, water is most dense at 4.0° C (39°F).  After the ice-off temperature, the vertical profile is all the same from top to bottom.  As the air temperature warms, the lake slowly warms, and temperatures at the lake surface gradually increase.  This increase will continue during the entire spring and summer. In June, the upper 5-8 meters will warm to such an extent that warm less dense water separates from the cooler, denser water. It is creating a layer that is a thermocline. The thermocline may become more profound as the summer progresses or stay at a depth of around 8 meters. The water below 8 meters will not circulate until fall turn over when the lake cools to the deep water temperature. Then the lake is isothermal and will re-mix or turnover. The deepwater is isolate from the atmospheric air and is cut off from oxygen. In the bottom sediments of the lake, active decomposition occurs that requires oxygen.

By August, in the deepwater zone, oxygen is depleted, which changes the water sediment zone’s chemistry at the bottom of the lake. The chemical changes in iron in an area without oxygen (anoxic)  causes the phosphorus bound to the iron to be released, creating phosphorus-rich water. This phosphorus water will stimulate green algae and cyanobacteria when the lake mixes in the fall.

In the winter, when ice covers a lake, deep layers of water without access to air may become devoid of oxygen and may lead to winter fish kills.  If there is an anoxic zone at the bottom of the lake, it will cause phosphorus release. Oxygen depletion in the winter is a slower process due to the low-temperature water. That photosynthesis continues under the ice when the ice is clear with limited snow cover.  Photosynthesis will produce oxygen. Under clear ice, Eurasian watermilfoil is seen topped out.

Spring and fall mixing are driven by wind, and prevailing wind direction changes by seasons, with more turbulent conditions occurring in the spring and fall. A typical dimictic pattern of temperature changes.

Before the ice melt, the lake’s oxygen levels are depleted. Springtime arrives, and the ice slowly melts with warmer temperatures exposing the lake water once again.  Stratification happens once again. The wind begins to mix the lake water, and the surface water begins exchanging gases with the air, pushing the surface water deeper and infusing it with oxygen.  Next time you are swimming in a lake, notice the temperature differences the deeper you dive down. If you have a swimming face mask on, you may see a layer of trapped debris and pollen at the zone of temperature changes.

When the lake turns over in the spring and fall, there is internal recycling of phosphorus from the deep water. The fall turnover recycles more phosphorus than the spring turnover. The spring ice melt also contributes phosphorus since most phosphorus is in the dust and dirt accumulating on the ice.  At the same time, there is increased runoff, so there is a slug of phosphorus and nitrogen compounds.

The green color is seen in the lake early spring, and late fall is due to green algae; if there is a white color, you have diatom blooms. If it like an oily sheen of green or a thick green soup, it may be a harmful algae bloom (HAB).  Below is a link to the New York State Department of Environmental Conservation  HAB identification website.

Algae blooms are nothing new to Saratoga Lake.  There are many types of algae, and most are harmless.  Algae generate oxygen through photosynthesis, providing oxygen in our atmosphere and forming the aquatic food chain that supports all the animals associated with lakes.