Since the river drops 250 metres (820 ft) over 112 kilometres (70 mi) to its mouth, whitewater canoeing is challenging, and extreme during spring conditions.

[2] The entire course of the Kesagami River lies within the Hudson (James) Bay Lowland and, like all other streams in that region, it flows with a swift current in a channel cut through the marine clay deposits overlying limestone rocks of Paleozoic age.

The thickness of the overburden diminishes as the river nears its mouth, and in places it flows over beds of horizontal limestone.

[3] The greater part of its course, which is generally in a north-northeast direction, is through a muskeg country with mostly dwarf black spruce and tamarack trees.

Owing to the amount of moisture in the ground, trees in this region do not attain a greater average height than about 9.1 metres (30 ft), and have a maximum diameter of 10 to 13 centimetres (4 to 5 in) in a growing period of between 100 and 150 years.