Marathon & the Middle Keys

A Marathon diving day is a morning or afternoon boat trip from a marina on the island. Captain Hook's Marina and Dive Center is at Mile Marker 53 on Vaca Cut and sends snorkel and dive trips out every day at 8:30 and 1:00, while Tilden's Scuba Center has its Marathon shop at Mile Marker 49.5 and runs to Sombrero Reef, Coffins Patch and the Thunderbolt. The reefs are within a 30-minute boat ride and Coffins Patch lies about 8 km (5 miles) out, so the boat rides are short, and Tilden's visits two sites on each trip. When the days are long Tilden's typically runs two-tank night dives.

Most of the diving is shallow. Sombrero Reef runs from roughly 2 m (5 ft) over its coral spurs to about 9 m (30 ft) in the deeper grooves, with brain and elkhorn coral, schools of yellowtail snapper, parrotfish and sergeant majors, and a good chance of sea turtles, nurse sharks and southern stingrays. Coffins Patch is six patch reefs with usually minimal current, and the Donut is one of dozens more patches beyond it. Visibility runs from about 3 m to 15 m or more on calm days (10-50 ft), and summer water sits in the 27 C range (80 F). Stony coral tissue loss disease has affected reefs throughout the Keys.

The Thunderbolt is the dive that needs planning. The ship has been collecting marine life since it was sunk in 1986 and sits upright and intact in 37 m (120 ft), where barracuda, mackerel, snapper, permit, jacks and resident goliath grouper gather, with the occasional black grouper and reef shark. Current can become considerable on the wreck, and with the depth that makes it an advanced dive: Tilden's wants to see previous deep experience in a logbook and takes no one under 15. Currents can also run around Sombrero Reef even on calm days.

Marathon suits new divers and snorkellers first: the patch reefs top out around 9 m, and Sombrero Reef and Coffins Patch are both Sanctuary Preservation Areas where fishing is banned. Experienced divers get one serious wreck in the Thunderbolt. Anyone travelling in hurricane season, May to September, should keep plans flexible.