Gravel (4 acres) and Spider (23 acres) islands comprise the Gravel Island National Wildlife Refuge. These islands are located in Lake Michigan, approximately 1 mile east of the northern tip of the Door County peninsula, Wisconsin. Along with Green Bay National Wildlife Refuge, Gravel Island Refuge is part of the Wisconsin Islands Wilderness Area, which, at 29 acres, is one of the smallest wilderness areas in the country. The refuge is managed by staff at Horicon National Wildlife Refuge, in Mayville, WI. Public use is not allowed due to ground nesting by migratory birds and limited access.