[4] It rises at an elevation of 670 metres (2,200 ft), flows south for about 80 kilometres (50 mi), and has two major tributaries.

[7] The drainage basin covers parts of two regional county municipalities, within which it covers parts of four smaller administrative units:[8] The name "Bouleau" (Betula) means birch, a tree that grows in cold and temperate regions, with white bark and small leaves, whose wood is used in carpentry, cabinet making and for the manufacture of paper.

The plateau has hills or ridges with steep slopes and is cut by valleys whose sides are over 350 metres (1,150 ft) deep in places.

The coastal fringe shows the influence of the postglacial Goldthwait Sea, which left large quantities of marine clay and silt sediments.

— (Balsam fir), dominant on the coastal plain and north of the watershed, and mixed spruce/fir in the central zone of the Bouleau River.

[11] There was a large infestation of hemlock looper moths (Lambdina fiscellaria) in the late 1990s and early 2000s that significantly damaged the fir trees.

About 6.85% of the basin is covered by water bodies, the largest being Lake Bigot in the north with an area of 9.1 square kilometres (3.5 sq mi).

[10] The network of streams and rivers is angular, conforming to fractures in the hard bedrock, with straight segments between right-angled forks.

About 4 kilometres (2.5 mi) above the head of the tidal area there is a long stretch of powerful rapids that may block the further upstream progress of Atlantic salmon.

[10] The river holds anadromous Atlantic salmon (Salmo salar), brook trout (Salvelinus fontinalis), and less commonly American eel (Anguilla rostrata) and three-spined stickleback (Gasterosteus aculeatus).

In view of the rapidly declining Atlantic salmon population catch-and-release should have been implemented on all rivers apart from northern Quebec.

[12] In 2017 all salmon, large and small, had to be released on the Malbaie (Gaspé Peninsula), Pigou, Bouleau, Magpie, Coacoachou, Nétagamiou, Little Mecatina and Véco rivers.