Lake Ontario is the easternmost of the Great Lakes and the final point in this massive freshwater system. Although it is the smallest of the five lakes by surface area, its deep basin holds a significant volume of water. This volume influences the climate and ecology of the surrounding region in the United States and Canada. Understanding Lake Ontario requires examining its precise physical measurements, especially its depth profile.
The Maximum Depth Measurement
The deepest point in Lake Ontario measures 802 feet (244 meters). This extreme depth is located in the eastern half of the lake, within a feature known as the Rochester Basin. The basin is situated in the central-eastern area, positioned between Rochester, New York, and Kingston, Ontario.
This maximum depth is substantially greater than the measurement for Lake Erie, which sits upstream. The Rochester Basin represents the lowest point in the entire lakebed, carved deep into the underlying bedrock. This measurement establishes Lake Ontario as the fourth deepest of the Great Lakes, surpassing both Lake Erie and Lake Huron.
Average Depth and Water Volume
The average depth offers a more comprehensive understanding of the lake’s overall shape and capacity than the maximum depth alone. Lake Ontario has an average depth of 283 feet (86 meters). This figure is greater than the average depth of Lake Huron and is second only to Lake Superior among the Great Lakes.
This profound average depth gives the lake its considerable water volume, despite its surface area of 7,340 square miles. The lake holds approximately 393 cubic miles (1,640 cubic kilometers) of water. This volume is striking compared to Lake Erie, which has a larger surface area but is significantly shallower.
Lake Ontario holds nearly four times the volume of water found in Lake Erie. This large volume contributes to the lake’s long water retention time, estimated to be about six years. The water stored in the basin acts as a thermal reservoir, influencing regional weather patterns.
Glacial Origins of the Deep Basin
The depth profile of Lake Ontario is a direct result of immense geological forces. The deep basin was carved out by the movement of continental ice sheets during the Pleistocene Epoch, specifically the Wisconsin glaciation. Prior to the ice age, the area was likely a pre-glacial river valley that provided a natural trough for the ice to follow.
The Laurentide Ice Sheet, which was up to two kilometers thick, scoured the bedrock, deepening and widening this trough. The erosion cut into the older, weaker Paleozoic limestones and shales that form the underlying geological structure. This prolonged glacial action resulted in the formation of a deep, U-shaped trench.
The deepest part of the lake floor sits far below sea level, a feature known as a cryptodepression. Since the lake’s surface elevation is approximately 243 feet above sea level, the maximum depth of 802 feet means the deepest point is about 559 feet below the ocean’s surface. The weight of the ice also caused the Earth’s crust to depress, contributing to the basin’s great depth.