(PORT AUSTIN) -- The federal government is suing a tiny Michigan museum to recover a 19th-century lighthouse lens that helped ships navigate Lake Huron. The 900-pound lens, built in France, has been displayed since 1987 at a former life-saving station at the tip of Michigan's Thumb. The government is objecting because it doesn't have an agreement with Huron City Museums. The U.S. Coast Guard donated the lens to the city of Harbor Beach in 1970 under certain conditions. The city later let Huron City Museums, near Port Austin, use it. The government's lawsuit in Bay City federal court says the lens is "irreplaceable" yet it's being housed in a building with no alarm or fire sprinklers.