Translated "shining water" Lake Ontario at 193 miles long and 53 miles wide is the smallest of the Great Lakes. However, at a depth of 802 feet it is the third deepest of all the lakes. Throughout the history of North America, Lake Ontario has played an important role for both early native cultures and early European explorers. Although Lake Ontario is considered the smallest of the Great Lakes it receives water from one of the most powerful energy generating waterfalls in the world -- Niagara Falls. .