The River, also known as the Tunnel River or Bridge River, is a section of water located between the Main Biome and the Safari. It is cyan and deadly, like the surrounding Ocean, and leads into the River Tunnel. When the bridge is lowered into the Lone Cave, it carves a hole in the river floor.
The river can be swam across if perfectly jumped off of the edge of a raised Bridge. The only other way to get across the river is to lower the Bridge.