Sand Beach (for saltwater swimming) and Echo Lake beach (freshwater) are the two places in Acadia National Park guarded by lifeguards during the Memorial Day to Labor Day season, and both are part of the Maine Healthy Beaches network.
The 237-acre Echo Lake, nestled in a scenic wooded area at the base of the Beech Mountain cliffs, has an average depth of 66 feet. Motors over 10 horsepower are prohibited here, but fishing (primarily for brook trout) is allowed outside the swimming area with the proper license.
Echo Lake is supposed to be on the ‘quiet side’ of Mount Desert Island, but anywhere from 10,000 to 15,000 people now show up in season. The beach certainly has the advantage over Sand Beach as far as water temperature is concerned (it’s 70° F. here, as opposed to 55° at best in the ocean), and lifeguards report that about 40% of the visitors to Echo Lake actually use their bathing suits (as opposed to 10% at Sand Beach).