Alternatively, the name may originate from "Mazinaa[bikinigan]-ziibi", Algonquian for '[painted] image river', referring to the pictographs found on Mazinaw Lake, though this is by no means proven.

It begins on the Canadian Shield (mostly gneiss and marble), and then, after Carleton Place, flows through limestone and clay plains.

[7] Most of the upper landscape is temperate deciduous forest dominated by sugar maple, American beech, and red oak.

At one time, the forests had much more eastern hemlock, but this was logged out to produce bark for the tanning industry.

As water levels slowly fall, conditions suitable for swamp forests occur.

The second portion of interest is the rocky, rapid-filled section of the river from Sheridans Rapids down to just past Playfairville.

Here there are small populations of unusual species including Parnassia glauca (Grass-of-parnassus), Platanthera flava (Tubercled Orchid) and Spiranthes lucida (Shining Ladies'-tresses).

Purdon Conservation Area supports Canada's largest native colony of showy lady slipper orchids, comprising about 16,000 plants.

In drier areas, there are several provincially significant alvars, limestone plains with exposed rock and many rare plants.