The river flows through the Uatuma-Trombetas moist forests ecoregion.

[2] The source of the Jari is in the south of the Tumuk Humak Mountains, and its mouth is at the Amazon River between the municipalities of Almeirim in Pará and Vitória do Jari in Amapá.

[4] The Jari River forms the western boundary of the Tumucumaque Mountains National Park.

Below the park it forms the western boundary of the 806,184 hectares (1,992,120 acres) Rio Iratapuru Sustainable Development Reserve, created in 1997.

Small numbers of people have settled along the river here, built houses and cleared fields.