This young iguana, only about 24" long, could reach 5-6' as an adult. It is bright green with brownish stripes and markings. Iguanas in different localities may vary in color, from blue to red, orange or black, and changing drastically with age. It has a row of spines all along its back to the base of its tail, and a row under it's chin, as well.
This youngster was in a tree overhanging the water, dropping into the lagoon when approached (a bad move because then it was easily nabbed by the canoeist). Usually diving into water is good protection against predation by hawks and eagles.
Iguanas are called "Gallina de palo" in Puerto Rico, (roughly, "tree chicken") and is a common item in the diet in some Central and South American countries. The Wikipedia entry for iguanas is excellent.