Caiman are not considered aggressive nor are they a threat to people, as they are not large enough to attack most mammals. Some locals will even swim near them. Nevertheless, I get all the swimming I need in the swimming pool at our condo or ocean in Tamarindo/Langosta, and I am not tempted to swim in any river or pond with a caiman.
I took this photo in Tortuguero National Park, which is on the northern Caribbean coast on the opposite side of Costa Rica from Tamarindo. I will post more photos from that tropical jungle in the future.