It defines the boundary between Peru and Brazil in the centre of the state of Acre, then runs for a short distance along the boundary of the 231,555 hectares (572,180 acres) Santa Rosa do Purus National Forest, a sustainable use conservation unit created in 2001 after it is joined by the Santa Rosa River.

[9] In the lowest reaches the river flows through the 1,008,167 hectares (2,491,230 acres) Piagaçu-Purus Sustainable Development Reserve, established in 2003, which holds a large part of its floodplain.

[citation needed] William Chandless found its elevation above sea level to be only 107 feet (33 m) 590 miles (950 km) from its mouth.

[11] Peckoltia brevis, a kind of catfish, is found in the middle and upper Amazon within the Purus river basin.

[14] In the municipality of Tapauá, Amazonas, the river flows through the 233,864 hectares (577,890 acres) Abufari Biological Reserve, a strictly protected area.