Why are the five great lakes of Ontario and four main in Manitoba smaller than they were glacial period?

There are only five Great Lakes: Lake Superior Lake Huron, Lake Michigan -which are connected, Lake Erie, and Lake Ontario. None of them are located in the province of Manitoba in Canada. All five border either the Canadian province of Ontario, or an American state. It seems like there may be a misunderstanding regarding either the location of the Great Lakes, or which lakes you were questioning the sizes of.