on this link, the institudo estadual do ambiente (inea)provides the suitability of several beaches on paquetá island, including the nearby praia dos tamoios, that can be used to estimate the water quality at praia do buraco.

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.      

this link shows praia do buraco on a wikimapia  - the link as we present it is best seen using google chrome.