Lake Iroquois, now Lake Ontario, was nearly the same depth as Lake Warren, now Lake Erie. As mentioned earlier, following the retreat of the middle Wisconsin Glacier a basin was created. This lake was called Lake Lundy. After the waters of Lake Lundy fell due to the rise of the land, it became a smaller lake named Lake Iroquois.
The depth of Lake Iroquois has fluctuated over the last few years. It was much lower when Iroquois beach was created. The shoreline of Lake Iroquois was carbon dated at approximately 12,000 years old.
During the life of Lake Iroquois, the northern shore rebounded at a greater amount than the southern shore. This resulted in the continual rising water levels along the southern shore. This caused increased erosion along the edge of the Niagara Peninsula. Lake Iroquois was a proglacial lake, meaning that the lake was situated between rock deposits and the ice front. The northern shore of this lake was the southern edge of the retreating glacier.
The waters of glacial Lake Iroquois were held back by the ice of the giant glacier, which stretched across the St. Lawrence valley to the east. The only outlet for this lake was at Rome and Utica, New York. The water exited to the ocean through the Mohawk and Hudson River Valley.
Later this route shifted to a route north of the Adirondacks through the Champlain Valley, which caused the water level in Lake Iroquois to drop 15 meters (50 feet). When the Wisconsin Glacier had retreated north of the St. Lawrence Valley, the lake’s water level dropped to sea level within several years.
Over the past ten thousand years, the lake water level has risen to its present level as the eastern end of current Lake Ontario continues its post glacial rebound uplift. More specifically in the past 100 years, the post glacial rebound at the eastern end of Lake Ontario has resulted in the water level at the western end of this lake to rise 0.3 meters.