The temperature of water at the bottom of a lake that is covered by a layer of ice depends on various factors, including the thermal conductivity of the ice, the depth of the lake, and the temperature of the surrounding environment. However, we can make some general observations.
Water has its maximum density at approximately 4 degrees Celsius. As water cools below 4 degrees Celsius, it starts to become less dense and expands. This is why ice floats on water. When the surface of a lake freezes, it forms an insulating layer of ice that acts as a barrier between the cold air and the water below.
Under normal circumstances, the temperature at the bottom of a lake below the ice layer will tend to approach 4 degrees Celsius. This is because water is a relatively poor conductor of heat, and the insulating properties of the ice layer prevent the transfer of heat from the colder air to the water below. As a result, the water at the bottom of the lake will be insulated from the freezing temperatures above and remain relatively close to its maximum density temperature of 4 degrees Celsius.
However, it's important to note that this is a generalization, and actual temperatures may vary depending on factors such as the depth and size of the lake, local climate conditions, and any geothermal or other heat sources that may be present.
In summary, the temperature at the bottom of a lake covered by an ice layer will typically be close to 4 degrees Celsius, assuming no significant heat sources or other factors influencing the temperature.