The lake's initial outlet was at present day Fort Wayne, Indiana, the lowest place on the border of the basin. Its altitude seems to have been at first about , or above the current level of Lake Erie, but during its life as an outlet, reduced to . At its highest point, the lake used this single outlet. Later, after further ice melt a northerly outlet was reached near present-day Imlay City, Michigan, and lake had two outlets for a short time.