What is a sealed bottom lake?

A sealed bottom lake is a lake whose sides and bottom are lined with a layer of impermeable clay, such as glacial till or alluvial deposits. This prevents the water in the lake from seeping into the ground and draining away, meaning the lake can retain water even during dry periods.

Sealed bottom lakes are formed in a number of ways, but the most common is through the deposition of fine-grained sediments in the bottom of a lake basin. These sediments, which are often derived from glaciers, rivers, or windblown dust, can form a layer that is impermeable to water. In some cases, a sealed bottom lake may also be formed by the movement of tectonic plates, which can cause the rocks at the bottom of the lake to become fractured and sealed.