No 1st hand experience
but
last winter at Baie Rouge saw several enter the water at the far right end [facing the water] and snorkel off to the right, they went around the rock cliff and we lost sight of them. They were away for an hour?

Baie Rouge - if driving from Marigot thru the lowlands, at some point the road makes a hard left trun, at that bend, a road runs straight ahead, follow that road 200 yds? and you are in a parking lot above Baie Rouge. An "attendant" will find you and take you to chairs [$20 for 2?] if no need for chairs, you might consider a small tip anyway as they patrol the car park

J&B