Brule Glacial Spillway State Natural Area preserves the upper Bois Brule River valley in three parcels within Wisconsin’s Brule River State Forest. The valley was carved at the end of the last Ice Age by the outlet of Glacial Lake Duluth, and its drainage later reversed as glaciers melted and Lake Superior fell. Near Solon Springs, a broad bog marks the Saint Lawrence River Divide, long used as a portage between waters flowing toward the Atlantic Ocean and the Gulf of Mexico. Because the valley remained close to pre-settlement condition, it retains rich wetlands, boreal habitats, rare plants, diverse bird life, and uncommon insects.