South of the paved roads, the river is the road. The korjaal is a long, narrow wooden boat with an outboard motor. Life jackets should be in the boat. Ask. The ride can be loud, wet, and sunny. A dry bag for your papers is worth more than another shirt.
The usual start for the Upper Suriname is the landing at Atjoni, after the long drive down the Afobaka road. Your host sets the departure. Low water changes where the boat can pass. High water changes the schedule the other way. Build a spare day into any route that depends on a boat.
Commewijne has a gentler version of the same idea: creek boats between former plantations, close enough to Paramaribo to be a day. The Coppename, toward Raleigh Falls, is the expedition version and usually starts with a flight, not a road.
While you are there
The landing is a working place. Stand where the captain tells you. Do not treat a passing village as a photo stop unless your host has arranged the visit.