at a glance

on this link, the instituto estadual do ambiente (inea) provides the suitability of several beaches in rio de janeiro. 

constantly updated, the red flags mean that swimming is not advisable, green flags mean waters are clean, and yellow flags suggest using own judgment. 

when referring to the inea's table, water suitability for praia de dentro is similar to praia da urca's water.

any of rio's beaches may show polluted waters within 24 to 48 hours following heavy rains.