Lake Tonawanda was a prehistoric glacial lake in western New York that existed about 10,000 years ago near the end of the last ice age. Formed as glaciers retreated and Great Lakes water levels stood higher, it lay east of the present Niagara River between early Lake Erie and Glacial Lake Iroquois, ancestor of Lake Ontario. Fed by elevated Erie waters, it drained north over the Niagara Escarpment and over falls that included one at present-day Lockport. It vanished when Lake Erie dropped too low to supply it, but its old bed still shapes the region through surviving traces of ancient falls and soft sediments that contribute to sinking homes in places such as Amherst.