Monkey River is a tiny village about an half hour boat ride south of Placencia. The village is home to approximately 30 families. Dive shops in Placencia offer tours into Monkey River town and then up the river into the jungle where howler monkey roam. After hurricane Iris they have gotten more scarce but the trip up a jungle river is engaging regardless.
Ocean Motion (mid way down the sidewalk) or Nite Wind (right on the corner by the main dock) both offer tours with experienced guides. If you're lucky you may get a trip through the mazes of the Mangroves.