on this link, the institudo estadual do ambiente - inea, provides the suitability of several beaches on ilha do governador, including praia da guanabara (praia da guanabara), that is somewhat close to praia da moça and can be 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.

any of rio's beaches may have polluted waters within 24 to 48 hours following heavy rains - while cleaning is underway, many of ilha do governador's beaches are normally not suitable for swimming.