The Lièvre River watershed is situated in the humid continental climatic zone. The southern portion of the watershed enjoys a mild climate, while the northern portion is colder and damper.

Accordingly, the type of dominant vegetation changes from south to north, covering a range of bioclimatic subdomains. The sugar maple-hickory subdomain is found exclusively along a narrow strip of the Ottawa River shoreline near the mouth of the Lièvre River, while sugar maple-basswood forests grow in the southern portion of the territory up to the sugar maple-yellow birch domain. Balsam fir-yellow birch stands cover the northern portion of the watershed and balsam fir-white birch, the northernmost tip. The latter borders the southernmost area of the boreal forest, which covers a large part of northern Canada.

Adapted from "Pour la qualité de l'eau du bassin versant de la Lièvre: PORTRAIT&", published by the Comité du bassin versant de la rivière du Lièvre (COBALI), 2005.