A small protected reef-and-islet group about ten minutes by boat from Coron town, Siete Pecados ("Seven Sins") is the easiest snorkel from the mainland — a healthy coral garden in shallow, current-protected water, with very high fish density. It is the standard first stop on most Coron island-hopping tours.
The marine park is run by a community cooperative and charges a small entry fee. Best in the morning before the wind picks up. Watch your buoyancy near the corals — the reef is now under more pressure than it would like.