Situated on a gentle promontory high above Lake Ontario's Bay of Quinte, Lake on the Mountain is a natural curiosity: it has a constant flow of clean, fresh water, with no readily apparent source. This mystery has been the subject of speculation for centuries. Mohawks believed that the deep, turquoise waters were home to spirits. Early settlers supposed that the lake was bottomless. Over the years, geographers and scientists have devised many complex theories about how the lake restores itself.

Today, the most generally accepted theory holds that the lake is a collapsed doline, an unusual feature found in areas with a limestone rock foundation. Dolines are cavities formed when limestone beneath the surface dissolves. Ultimately the roof collapses and the giant sinkhole fills with water. The lake's outlet stream flows northward through a shallow, bedrock channel, eventually tumbling over the Prince Edward Escarpment to the Bay of Quinte below.