Sombrero Reef

Sombrero Reef is a shallow coral reef and sanctuary area about four miles offshore from Boot Key near Marathon. The protected area covers 208 acres and has a triangular outline. This is a snorkel or dive trip, not a roadside pullout: reach it by boat, and don’t drive to the offshore map pin.

Below the surface, coral ridges alternate with sandy channels in a pattern called spur and groove. Depths in the protected area stay under 30 feet, and the reef draws visitors for snorkeling and diving. People often talk about fish, turtles and other marine life, though visibility and what you see vary with conditions.

The red skeletal tower of Sombrero Key Light stands where the reef meets open water. Built in 1858 and rising 142 feet above the sea, it is the tallest lighthouse in the Florida Keys. The tower is not an attraction to climb or visit on foot; see it from the water. For a photo, leave open sea around the light so the frame shows how far offshore it stands.

Boat excursions leave from the Marathon area, while the reef itself has no road or shore arrival. Open-water chop can make the ride or snorkeling uncomfortable, so conditions matter even on a sunny day. The 2023 marine heat wave caused widespread coral bleaching and mortality; older pictures can give a rosier impression of coral color and health than the reef can promise now.

Use a mooring buoy when one is available. In the protected area, do not touch or stand on coral, fish, or collect.