We were a little disappointed with Yalku two years ago. Didn't see as many fish as we anticipated, but perhaps our expectations were set too high. I think we also were swimming in the wrong spots. We concentrated on swimming out toward the ocean to see if we could find turtles. Didn't see much out there except a ray, which was really cool. We got there first thing in the morning, and for the first hour and a half we had the whole lagoon to ourselves. It was really peaceful. We left when some groups arrived, and then went to Akumal Bay, which was really cool.