This is a large S Am rodent imported for its fur (that quickly lost any useful fur in the warm climate, but continues to devour the native aquatic vegetation). Still a cool critter.
They've finished mating per se; now the male is mate-guarding -- continuing to hang on to her while she oviposits. We saw her dipping her tail repeatedly in the water (caught in the act in the shot below).
I think this is probably Sympetrum fonscolombii (Red-veined Darter).
The brochure just gave Swamp Turtle as the common name; think I've got the right ID.