Gravel (4 acres) and Spider (23 acres) islands comprise the Gravel Island National Wildlife Refuge. These islands are located in Lake Michigan, east of the Door county peninsula. Along with Green Bay National Wildlife Refuge, Gravel Island Refuge makes up the Wisconsin Islands Wilderness Area. The refuge is managed by staff at Horicon National Wildlife Refuge, in Mayville, WI.

Neither Gravel nor Spider Island has any permanent vegetation remaining. Spider Island has lost the remnant forest which existed there as late as the 1970s. All of the trees have fallen over or been washed away. Waterfowl use on the islands is very limited since there is very sparse vegetation. However, the fallen trees provide some cover for scattered nesting of dabbling duck species like mallards and black ducks, as well as Canada geese. The number of waterfowl nests do not exceed 15 to 20 in one given year. Spider Island supports colonies of herring gulls and double-crested cormorants. One pair of black-backed gulls has successfully nested on Spider Island the last several years. Other incidental species nesting or using Spider Island include Canada geese, red-breasted mergansers, mallards, Caspian terns,and an occasional peregrine falcon. Gravel Island has nesting herring gulls, double-crested cormorants,and a few nesting ducks.

Public use is not allowed due to ground nesting by migratory birds and the limited access.