Question regarding the lagoon at Barra de Potosí

OK, I have another thought. We have swam in a number of rivers in Mexico, the first time we had issues with bites was in the Usumacinta, between Chiapas and Guatemala. Everyone was swimming, and they laughed at us when we reacted to the small, guppy sized fish biting us! Not really bad, but an eyeopener We have run into them in other rivers and river mouths too.