Check out this satellite photo (zoomable)http://www.mapygon.com/canada/ontar...aunt-lake/
And here's the full Google versionhttp://maps.google.com/maps?hl=en&q...7&t=h&z=13
Light colored areas should be shallow...compare to what you already know.
One more thought...contact the Ontario Fisheries folks. If a map of the lake does exist....they should be able to tell you.