Link to Grindstone photos Grindstone Lake, located in Pine County 6 miles west of Sandstone, is one of the deepest lake basins in Minnesota and is an anomaly in a region dominated by 6 to 12 m deep lakes. The lake basin was scoured out by glacial erosion which removed sedimentary material that had been deposited in the pre-glacial bedrock valley. Grindstone is long and narrow, about a half mile wide, 2 miles long, and very deep. The deepest hole is 47 m deep. The lake has an average depth of 22 m, much deeper than any other lake in this region. See the lake summary tables for additional watershed and water quality information. See data summary-limnology overview for an overview of Grindstone Lake for 1999. The lake's watershed area of 5,079 ha (12,544 acres) is primarily undeveloped, consisting primarily of forest, wetland, water, and agriculture. Most of the homes are along the north, west, and south ends of the lake. The eastern shore has very little development. Grindstone is a "two-story" lake, meaning it contains habitat for both warm and cold water fish. The lake originally only had only warm water fish but has been stocked and maintained as a trout fishery. The trout are able to live in the deep, cold regions of the lake because oxic (containing oxygen) conditions persist down to ~33 m, even through the summer months. The Grindstone RUSS will be maintained by the MN DNR Fisheries Office out of Hinckley and by the Audubon Center of the North Woods. See the collaborator page for local staff and contact information.