Many of Montreal's marinas and yacht clubs, including the highly regarded Royal St Lawrence Yacht Club, lie on the shores of Lac St Louis. However, the chart warns "that numerous depths shoaler than charted exist outside of the main channel" . This coupled, with the fact that the Lake is experiencing historicually low water levels, means that if you are in a deep draft yacht then most, if not all all, the marinas on the lakes may be off limits to you, especially later in the summer when lake water levels are lower.
However, in settled conditions, reasonable deep draught yacht anchorages may be found around the shores of Ile Perrot at the western end of the lake. La Grande Anse on the NE shore of the island is the most obvious, but for any vessel drawing more than 1.0m involves a 10 mile round trip to get there from the main seaway as the direct channel is too shoal. Alternatively you can anchor just about anywhere of the SE coast between the island and the main seaway channel in 4-8m of water with good holding on mud. The currents outside the main channel should be less than 0.5 knot so swiming from the boat is a possibility in these anchorages.
The charted anchorage area closer to the Beauharnois lock and hydroelectric dam are exposed to the full strength of the stream and the bottom has been scoured to rock in many areas and is less suited for yacht anchoring.