Alligator Reef

In November 1822, the USS Alligator — a U.S. Navy schooner on patrol to suppress piracy and protect merchant convoys in the Caribbean — ran aground on a shallow reef four miles off what is now Islamorada. Unable to free the ship, and unwilling to leave her for pirates to pillage, the crew burned and sank her deliberately. The reef has carried her name ever since.

Two hundred years later, two piles of ballast stones near the site are traditionally identified as the remains of the Alligator — though a 1996 expedition raised questions about that attribution, suggesting the wreck may belong to a different 19th-century vessel entirely. Either way, something went down here, and the story is part of what makes this one of the more layered dives in the Keys.

The Alligator Reef Lighthouse was completed in 1873 — a 136-foot iron skeleton tower driven into the coral to warn sailors of the same hazard that claimed the USS Alligator. It's still standing, black and white against the sky, visible from the shore on clear days. For decades it was an active navigational light; now it's a landmark, a community symbol, and one of the most photographed structures in the Florida Keys.

Below it, the reef has had two centuries to develop undisturbed. As a designated Sanctuary Preservation Area within the Florida Keys National Marine Sanctuary, anchoring directly on the reef is prohibited — the site is accessed via mooring buoys only, which has kept the coral intact and the marine life abundant. Surveys have documented over 500 species here. In the water, that number is easy to believe — Nurse Sharks rest under ledges, Goliath Grouper hold the deeper areas, Turtles move through with the unhurried ease of animals that have never been harassed, and fish life layers the water column from the coral surface to just below the boat. For IDC's afternoon trips, it's a regular stop and consistently one of the most memorable dives guests take in Islamorada.