Tenacatita [1]’s hinterland is a spreading wildlife-rich mangrove marsh. From a lagoon-side landing inland from the Tenacatita dune, you can float a boat, rubber raft, or canoe for a wildlife-watching excursion.
Local guides (ask for Adan at restaurant Chito) furnish boats and lead trips ($30) from the same spot. Animals often viewable are coatimundis, crocodiles, iguanas, ilamacoa (boa constrictors), and flocks of herons (grey and white), cormorants, anhingas, and much more, especially in the winter. Take your hat, binoculars, camera, telephoto lens, and plenty of insect repellent.
Links:
[1] http://www.moon.com/destinations/puerto-vallarta/the-jalisco-coast/road-trip-barra-de-navidad/playa-tenacatita