Six Mile Lake, at the southernmost extremity of the Canadian Shield, has all the typical aspects of the Shield including rocky barrens, scrub wetlands, and weathered, granite promontories crowned by weathered pine trees.

The park is part of the Great Lakes-St. Lawrence lowlands forest region. The mixed forests here include oak, maple, poplar, birch and white pine trees. Hundreds of plants have been identified in the park, including three species that are rare in Ontario -- pondweed, yellow-eyed grass and smartweed.

The rock barrens, forests and shrub wetlands of the area provide habitat for chipmunk, raccoon, beaver and white-tailed deer. Red fox and black bear also live here.

Birdlife is abundant, both in the forests and the marshy areas. Ninety-one species have been identified, including the wood thrush, pileated woodpecker, great blue heron, turkey vulture and loon. Rarer species sometimes sighted are the yellow-throated vireo and Swainson's thrush.

An unusual insect found here is the walking stick, which will disguise itself as a small twig for protection. The park is also home to various harmless snakes and the rare five-lined skink, a small harmless lizard. The massassauga rattlesnake, the only poisonous snake in Ontario, inhabits the area but few campers encounter one.