That doesn't mean it's chilly: January sees the lowest average temperature of any month, but that low is a mild 65 degrees Fahrenheit. Wintertime weather in the Keys is pleasant, but the water is also at its coldest during these months, so you may need to work a shortie wetsuit into any diving or snorkeling plans.

Snorkeling in the Florida Keys in January is entirely possible, but whether it is "too cold" depends on your tolerance and the weather on the specific day. The water temperature in January typically averages between 70°F and 74°F (21°C to 23°C). While this is significantly warmer than the ocean in the northern U.S., it can feel chilly if you are submerged for an hour, especially when you factor in the wind chill on the boat ride back to shore. Most professional snorkel charters in Key Largo or Islamorada offer wetsuit rentals (usually 3mm shorties), which make the experience much more comfortable by trapping a thin layer of warm water against your skin. The bigger challenge in January is not the temperature, but the wind and sea state. Winter cold fronts can bring choppy water and reduced visibility, making it harder to see the coral reefs at John Pennekamp State Park. If you visit on a calm, sunny day in January with a light wetsuit, you will find the reefs less crowded and the marine life just as active as in the summer months, making it a great "off-season" adventure for hardy swimmers.