Swimming with the fish and turtles in this sublime stretch of slow-flowing blue water amid the desert landscape of the Cuatrociénegas nature reserve is a surreal, revitalizing experience. There are palapas (thatched shelters), picnic tables and even a snack bar. Several sets of ladders and steps lead visitors into the water (or do as the kids do and cannonball in).
You can also hire kayaks (from M$150 per hour), for a paddle along the meandering, crystal-clear waters. Last visitors admitted at 5pm. From town, look for the turnoff just before the Poza Azul Visitor Center.