this link shows praia do preventório on a wikimapia - the link as we present it is best seen using google chrome, as it might not open correctly with other browsers.  

on this link, the institudo estadual do ambiente (inea)provides the suitability of several beaches in niterói, including praia de charitas, that can be used to determine water quality at the praia do preventório since they are near each other.

constantly updated, the red flags mean that swimming is not advisable, green flags mean waters are clean, and yellow flags suggest using own judgment - any of rio's beaches may have polluted waters within 24 to 48 hours following heavy rains.