The Represa de Promissão, officially known as the Usina Hidrelétrica Mário Lopes Leão reservoir, sits on the Rio Tietê in the interior of São Paulo state, near the municipalities of Promissão, Ubarana, and Avanhandava. The reservoir covers approximately 530 km², making it a substantial body of water with considerable open stretches. The dam itself spans 3,630 meters in length, and the impoundment holds roughly 2,128 km³ of water.

The reservoir forms part of the Hidrovia Paraná-Tietê, an inland waterway system, and is equipped with a navigation lock that allows vessel passage. This means paddlers share the water with commercial and recreational boat traffic associated with the waterway, which is a relevant safety consideration when planning routes or crossing open sections of the reservoir.

The site has been in operation since 1975 and is currently managed by Auren (formerly AES Tietê). Beyond power generation, the reservoir is used for leisure activities, fishing, and general navigation, indicating some level of public access and recreational use. Details about designated put-in and take-out points, paddling regulations, facilities for paddlers, water quality, and seasonal conditions vary and should be confirmed directly. Paddlers planning a trip here should contact local authorities or the reservoir operator directly to confirm current access arrangements and any restrictions that may apply to non-motorized craft on this working hydroelectric impoundment.