The Rio Pereque-Acu is a river in Rio de Janeiro state, southeastern Brazil, flowing into Ribeira Bay near the historic town of Paraty at approximately 23°13′S 44°43′W. The river passes through mangrove forest, with Rhizophora mangle among the vegetation along its banks, giving it a distinctly coastal, estuarine character as it approaches the bay.

The river is used as part of a popular kayaking circuit departing from Paraty's old town. One well-established route follows a circular course from the old town beach, passes the fort, continues through the mangroves, and returns to the starting point via the Pereque-Acu. This route is offered by guided kayak tour operators based in Paraty and is accessible to paddlers using both single and double kayaks. The combination of open bay paddling and mangrove channels makes it a varied outing.

Wildlife along the river includes capybaras, which have been observed in groups on both banks. The mangrove environment likely supports additional fauna typical of coastal Rio de Janeiro.

The river also carries historical weight: the earliest settlement of Paraty — one of Brazil's best-preserved colonial towns and a UNESCO World Heritage site — was established on a hill to the north of the Pereque-Acu, making the river a boundary marker in the town's founding geography. Paddling the river therefore places you alongside centuries of Brazilian colonial history.

Guided tours operating on this route can provide dry bags and secure storage for valuables. The river has served as both an embarkation and disembarkation point for water trail operators working out of Paraty.