Hello @ nameless-berk: after making a search through the comparison of photos in lagoons of the Dominican Republic, I came to the conclusion that the photo you show corresponds to "La Laguna Hoyo Claro" (Natural Monument), located in the Verón-Punta Cana highway. A wetland ecosystem that shelters a semi-humid tropical forest. The monument includes an area with lagoons, grasslands and forests of palm that is found in the coastal plain of the referred region and how much with an extensive swamp. (http://www.arecoa.com/videos/2017/05/30/monumento-natural-hoyo-claro-otro-encanto-de-punta-cana/)

http://www.idominicanas.com/hoyo-claro-un-espectacular-monumento-natural-en-punta-cana/
I imagine that the blue color of these waters comes from a few meters underground where it is heated by natural way and that it must have a high mineral content, what gives it that typical color, and that perhaps it becomes an element of high power healing.
Greetings.