Barra del Colorado Wildlife Refuge

The two sides of the river are remarkably different. The Nicaraguan side is covered with dense primary forest, in sharp contrast to Costa Rica's side, where the forest has long ago fallen before the chainsaw and what remains are big wetland forest and swamps, that become vast alluvial floodplains during the rainy season.

The wildlife here is varied,  large populations of monkeys and birds can be see throughout the park. There are also some unusual amphibians which abound on the banks of streams, like the smoky and the glass frogs.

Take advantage of the chance to explore this wilderness area throughout many days, either if you are an experienced explorer or not, there are guides and plenty of room where to camp and  many wet portions of the reserve remain largely untouched. 

One interesting phenomenon peculiar to the San Juan River is the migration of Bull Sharks, from the Atlantic Ocean upriver to Lake Nicaragua. It's not clearly known why these relatives of the great white shark make the trip or how they adapt to the salinity changes in the water.