It flows in a generally north direction, and enters the Atlantic Ocean just past Marapanim, Pará, which lies on its left bank.

[1] The eastern side of the Marapanim Bay before Maiandeua Island is protected by the 30,179 hectares (74,570 acres) Maracanã Marine Extractive Reserve, created in 2002.

Further south the eastern side is protected by the Cuinarana Marine Extractive Reserve.

[1] The western side is protected by the 26,465 hectares (65,400 acres) Mestre Lucindo Marine Extractive Reserve, created in 2014.

[3] The area around Rio Marapanim has a low population, with about 18 people per square kilometre.