A map of the Ecological regions of Quebec places the lake in the 6J-T ecological subregion, part of the eastern spruce/moss domain of the boreal zone.

[8] The main tributary of Lake Walker is the Schmon River, which enters at the northern end.

[9] Like many of the lakes in the region, Lake Walker is highly elongated, being 33 km long and no more than 4 km wide, and has steep rocky sides.

A 2019 survey established its depth at 271 metres,[10] making it the deepest lake in Quebec, ahead of the Pingualuit crater in Nunavik (252 m).

The southern tip of the lake flows into the Aux Rochers River which carries its water to the Saint-Lawrence River about 30 km to the southeast.