Fleetwing Wreck

The dominant hazard on Great Lakes wrecks is cold water — surface temperatures may reach the 70s F in summer, but divers pass through two or three pronounced thermoclines and find the water perpetually cold (often 34-50 F / ~39 F constant) at the depths where wrecks rest, so hypothermia and the physiological effects of cold are a constant concern. Many of the most spectacular wrecks lie deep (70-110+ ft) where little sunlight penetrates, making them dark, cold dives that demand depth, gas-management and dark-water/low-light skills; penetration into intact hulls adds silt-out (loss of visibility from disturbed sediment) and overhead-environment entanglement risks on collapsed rigging, lines, fishing nets and monofilament left by anglers, so a cutting tool and disciplined buoyancy/finning are essential. Surfaces on infested wrecks are encrusted with sharp zebra and quagga mussels that can cut hands and gear, and divers should not scrape them off (it does not reliably keep them away and harms the wreck). Open-water lakes bring sudden weather changes, building seas and chop that can strand boats or complicate ascents, plus recreational and commercial boat traffic over popular dive sites, so surface marker buoys and clear surface-support communication are advised. Finally, all of Wisconsin's historic shipwrecks are held in public trust and protected by law: divers may not remove, deface, displace or destroy any artifact or structure from a wreck on public lands (Wis. Stats. 44.47 and 29.05), with violations punishable by fines up to $5,000 and seizure of boats and equipment; looting is reported to (800) TIP-WDNR.