In Puerto Aventuras, we did a Dolphin Discovery where you get to swim with dolphins. 
It was an adventurous excursion involving animals, nature and science. We sat through a brief video training first and then literally immersed ourselves into this experience!
We went through a rotation of getting to touch the dolphins and get more comfortable with each other. I did this activity with my two elementary aged sons. The younger son wasn’t quite big enough (weight wise) to do the dolphin ride successfully because the dolphins have to be comfortable with the size of child. But…after several attempts, he “supermanned” !
It was a really unique experience to interact so closely with these special animals. Touching them, riding them, being pushed up into the air in the stream. It was a leap of faith!
www.dolphindiscovery.com/mayan_riviera/rivieramaya-activities-dolphin-swim-adventure.asp
I highly recommend this experience. You can order photos through the company and a video of your experience. We also walked through an aviary of tropical birds and got to hold those as well!