Dives off Marathon
The red steel lighthouse at Sombrero Key is the tallest of the series built in the 1850s, and standing at 160 feet, it makes this dive spot very easy to find. The lighthouse is anchored right into the reef, as are all of the 1850s lighthouses built by the Army Corps of Engineers. There are some good spur-and-groove coral formations here, and one of the best things about Sombrero Key diving is what is called the Arch, where the coral forms a little arch through which you can swim and take underwater pictures. Lots of elkhorn and staghorn coral here, and lettuce coral too. Barracuda like Sombrero Key, and they seem to come here in groups, which is fun to see underwater.
Sombrero Reef is located four nautical miles from Marathon, FL in the Middle Keys, and it's a Sanctuary Preservation Area (SPA) so be gentle on the coral and as always do not touch any coral. Catch & Release fishing is allowed here. Visibility is usually 30 to 60 feet, and the areas you will most want to dive lie in depths ranging from 15 to 35 feet.