I just read on the Friends of Akumal Bay page on Facebook that the new Profepa rule states that all fins are now banned from snorkelers at Akumal Bay.  This reportedly includes all tour group members as well as guests staying at the resorts.  Wow.  Fins disturb the sand which prevents the sun from nourishing sea bottom grasses as well as potentially damaging coral beds, so looks like the new rule makes sense for the turtles but may present a different kind of snorkeling experience for vacationers.