Not only is it filthy, but you get one window in August where maybe, just maybe the water will climb up to 21 or 22 celsius. If you want nicer water, you gotta go to Wasaga, but then Geogian Bay is usually around 19 degrees.
You obviously have little to no knowledge of Lake Ontario. You talk as if the whole lake shares the same cleanliness and temperature characteristics as Toronto harbour. Ever hear of sandbanks? It is probably one of the nicest beaches in North America and the water is water enough to swim in by mid-June.