Anchoring in the islands near Gananoque usually means weeds and mud. Farther east toward Rockport, you might anchor in deeper water with rock and weed. There are many places to anchor the for the day, so I will just mention a few favorite night anchorages. There are good places to anchor if the docks are full.
Boats take a line ashore to limit their swing when it gets crowded.
Many boats anchor east of the island, but be sure to set an anchor light as it is near a favorite route to Gananoque. There is always plenty of anchoring room east and south of Beaurivage Island if you don't mind the wakes from the channel. A small day fee allows you to use shore facilities. Sadly, recent changes to protect plants have resulted in removal of many garbage cans and docks. East of Mulcaster Island is a bay to anchor, but it is getting more crowded as others discover it.