Eleven thousand years ago, the continental glacier that covered much of Ontario began to melt, forming ancient Lake Algonquin, which later receded into present-day Lake Huron. Today, Arrowhead is characterized by two distinct areas formed above and below the ancient waterline. The rocky upland above the waterline is rugged country with hardwood forest typical of the Canadian Shield; the area below is low-lying and sandy. Visitors to Arrowhead may trek across the ancient beaches of Lake Algonquin.

Ojibway people once hunted here, and deer and moose are still seen in the region. Growing in the shallows of Arrowhead Lake is the aquatic arrowhead plant which gives the park its name. The bright crimson cardinal flower is one of several uncommon southern plants that grow in the sheltered valley of the Big East river.