Tobermory — Fathom Five

Diving here is charter-driven and short-range. Boats leave the village harbour for two-tank runs out to the islands, morning and afternoon, and the crossings are measured in minutes rather than hours. Parks Canada requires divers to register before their first dive, which comes with a briefing on what is and is not allowed on the wrecks. Big Tub is the exception to the boat schedule, a roadside entry you can dive on your own time, though it shares the water with heavy tour-boat traffic and the access rules there are worth checking before you plan around it.

The escarpment carries on underwater as bare grey dolostone: sheer faces, undercut ledges, cracks wide enough to swim into and boulder fields piled at the base. Almost nothing overgrows it, so the rock reads like quarry stone and the light stays hard until depth takes it. Thermoclines arrive abruptly. The surface layer warms through the middle of the season while anything deep stays close to single figures whatever the date, and that, rather than the air temperature, is what decides your suit.

The detail is what makes the cold worthwhile. Fresh water has no shipworm, so planking, deadeyes and windlasses still read as carpentry rather than as reef, and fittings sit roughly where they were left. Invasive zebra and quagga mussels now coat most exposed surfaces, and their filtering is generally credited with part of the clarity divers come for. The shallow hulls sit in enough light to snorkel over, while deeper down a torch is what makes frames and fittings legible again.

It suits wreck divers, drysuit divers and anyone more interested in wooden shipbuilding than in marine life, and it works for mixed groups because the shallow sites and the deep ones sit close together. Build in spare days: Georgian Bay can shut down the offshore boats, and when it does, the harbour and the shallower wreckage inshore are what is left. The workable window is a few months at most and the village is busy through all of it, so book charters and beds well ahead.