These islands are composed of erosion-resistant rock that protruded above the water after retreating glaciers had carved out the basin that holds Lake Michigan.

[2] Hog Island is approximately 4 miles (6.5 km) long in a north-south direction, and lies off the shore of Emmet County, Michigan.

Its low, swampy terrain is of significant interest to naturalists because it is one of the least-disturbed islands in Lake Michigan.

[3][1][4] The island's wetlands are important spawning grounds for yellow perch and smallmouth bass, as well as lake birds that feed on fish, such as the common tern, listed as threatened within Michigan.

[1] Three endemic riparian plant species, Houghton's goldenrod, the Lake Huron tansy, and Pitcher's thistle, have been identified on Hog Island.