on this link, the institudo estadual do ambiente - inea, provides the suitability of several beaches on ilha do governador, including praia das pelônias, which is on the same side of the island as praia do saco pinhão, and can be loosely used to guess water quality.

constantly updated, a red flag means that swimming is not advisable, a green flag means waters are clean, and a yellow flag suggests using own judgment.