One bird that I saw quite often while being in Peru coast and ponds nearby was the Neotropic Cormorant. These birds are excellent swimmers and divers. They love to hang out in groups as well as for fishing. Let me give you some more information from © Wikipedia:
The Neotropic Cormorant or olivaceous cormorant (Phalacrocorax brasilianus) is a medium-sized cormorant found throughout the American tropics and subtropics, from the middle Rio Grande and the Gulf and Californian coasts of the United States south through Mexico and Central America to southern South America, where he is called by the Indian name of “bigua”. It also breeds on the Bahamas, Cuba and Trinidad. It can be found both at coasts (including some mangrove areas) and on inland waters.
Its diet consists mainly of small fish, but will also eat tadpoles, frogs, and aquatic insects. Information about its prey is sparse, but inland birds seem to feed on small, abundant fish in ponds and sheltered inlets.
© HJ Ruiz – Avian101