Standing four nautical miles off Islamorada in the Upper Florida Keys, the Alligator Reef Lighthouse rises 136 feet above turquoise waters as a monument to maritime survival and engineering ingenuity. Completed in 1873 at a cost of $185,000, the beacon was built to guard mariners against the treacherous coral shoals that fringe the Florida Straits.
The reef takes its name from the USS Alligator, a U.S. Navy schooner tasked with anti-piracy patrols that ran hard aground here in November 1822. Rather than abandon the vessel intact to salvagers or buccaneers, her crew blew her up where she lay. Half a century later, the U.S. Lighthouse Board selected the location for a permanent sentinel.
Because the underlying substrate consists of soft coral rather than bedrock, engineers utilized a screw-pile and pile-and-truss skeletal system. Massive iron piles were driven directly into the reef, allowing storm surges and hurricane waves to pass through the open framework rather than crashing against a solid wall. Originally housing a massive first-order Fresnel lens, the light guided shipping traffic for over 140 years before being decommissioned by the U.S. Coast Guard in 2014.
In recent years, the community non-profit Friends of the Pool Inc. secured ownership of the aging tower to lead its ongoing preservation. Today, the surrounding shallows serve as a premier snorkeling and diving destination, drawing boaters to explore vibrant spur-and-groove coral formations, sea turtles, and nurse sharks lingering directly beneath its historic iron footings.