Lake Ontario is quite small, with a length of approximately 311km (193 mi), and a breadth of 85 km (53 mi). If not for a greater average depth (283 feet, giving it nearly 393 cubic miles to Erie's 116), it would be most equal to Lake Erie where volume is concerned, as the two are quite similar in size with Erie coming out just ahead in both length and breadth. Given the volume of Lake Ontario, it's not too entirely surprising that the drainage basin covers a fairly large portion of Ontario as well as bits of New York, and extends as far down as Pennsylvania. There is a much greater population on the Canadian shores of the lake (there is about 726 miles of shoreline all together), as opposed to the U.S. side, and there is also an abundance of farming and industrialization on Canadian soil in the area.

The problem with this great lake is that it happens to be the last in the chain, and thusly, ends up accumulating pollution from all of the others before it. Sadly, it is no longer the cleanest lake, perhaps even the worst off at this point.

info gathered throughout high school geography classes, as well as, more recently, www.great-lakes.net.