The biggest creature found in Lake Ontario is the Lake Sturgeon (Acipenser fulvescens). These prehistoric-looking fish are the largest native fish species in the entire Great Lakes system. An adult Lake Sturgeon can grow to be truly "monstrous" in size, reaching lengths of up to 7 feet and weighing as much as 300 pounds. Often referred to as "living fossils," sturgeon have bony plates called scutes instead of scales and have been swimming in Earth's waters since the time of the dinosaurs. While they were once nearly driven to extinction by overfishing and habitat loss, massive conservation efforts in 2026 have led to a slow but steady recovery of the population in Lake Ontario. They are primarily bottom-feeders and are known for being very long-lived, with some individuals reaching over 100 years of age. While there are occasional "lake monster" sightings in Lake Ontario (locally dubbed "Kingstie"), marine biologists confirm that any large, dark shape seen breaching the water is almost certainly a massive, ancient Lake Sturgeon going about its business.
Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north, west, and southwest by the Canadian province of Ontario, and on the south and east by the U.S. state of New York. The Canada–United States border spans the centre of the lake.