unfortunately, while cleaning-up efforts are underway, many of the beaches in the sepetiba bay are normally not often suitable for swimming. 

getting to the beaches in the baía de sepetiba (sepetiba bay)can take two hours each way from rio's zona sul, and we recommend starting the day very early due to intense traffic.

for first time visitors, the best way would be via taxi, which could be expensive unless divided 4-way - the maximum number of passengers allowed in a taxi.