June 1929. There was a tense silence in the pilothouse as Captain Greene’s gaze fixed on the echo sounder of the U.S. Coast Guard survey vessel Margaret. "The thing must be registering erratically," he muttered. Moments before, the equipment had monitored depths in the hundreds of metres, and now suddenly it registered only 15m (50 ft.)–far too shallow for this part of Superior. It was virtually at the Lake’s east-west midpoint! Captain Greene ordered the vessel’s course retraced. The equipment once again registered extreme depths and then immediately shallow depths of 13m (43 ft.).

The Margaret had stumbled upon a hidden danger: a mountain of rock thrusting up in some parts within metres of the surface. A chill ran though the men. Sitting directly in the shipping lane between Thunder Bay and Sault Ste. Marie these rocks might offer an explanation for some of Lake Superiors mysterious ship disappearances... vanishings such as the Inkerman and Cerisoles.

The French minesweepers Inkerman, Cerisoles and Sebastopol, were built at Fort William. On November 13, 1918, they set from Thunder Bay to France and manned by experienced sailors. Sebastopol arrived safely while the other two ships were never seen again. In spite of the fact that both carried wireless equipment, no radio message was ever recorded. The year after they vanished, a body washed up on Michipicoten Island. Many years after that, skeletal remains were found east of Port Coldwell. Both were believed to be crew from the French boats, but were hastily buried before official confirmation. Adding to the mystery , none of the usual flotsam was ever found.

An intriguing conspiracy theory even developed. Two weeks after the minesweepers left Thunder Bay, an executive of Canada Car, builder of the minesweepers, allegedly claimed the ships had sailed through the Sault locks safely and made Port Colborne on Lake Ontario. When asked why no record of their passage could be found he replied that the captains had simply neglected reporting it, an unlikely explanation. The French Navy also reacted peculiarly. Asked if France had given up hope of ever seeing the ships again one official merely shrugged. This raised suspicion that the vessels were never lost, but had steamed directly across the lake to an American port as a result of some clandestine agreement between the French and Americans. A number of speculations floated around: the boats were shoddily constructed, they were sabotage (after all this was war-time. And now the Superior Shoal joined the list.

A year later, in 1930, when the Canadian Hydrographic vessel Bayfield arrived to survey the Margaret’s find, the crew had the unsettling feeling of sailing over a veritable graveyard.. A course variation of only 5 kms (3 miles) meant the difference between a depth of 300m (1,000 ft.) and a potentially deadly one of only 6m (21 ft.) beneath the surface.

In the Bayfield’s first attempt to discover what wrecks might be clinging to the rocky incline, her grappling hook took hold of rigging from a sunken ship, but failed to raise it. The crew did manage to bring an unidentifiable fire-axe and tangled fishing net aboard. The net exposed another entire dimension to the story–motivated by greed, fishermen had kept the existence of the shoal secret for decades.

It turned out fisherman had their own lore about Superior Shoal. There were tales of phenomenal catches, one claiming that an amazing single-run haul of three tons was unsaleable because dealers complained the fish had a peculiar flavoured. Rumours spread that fish caught on the shoal having revolting mutations and protruding teeth,. Before reaching market they had to be decapitated. While conducting its survey, the Bayfield’s crew noted a tug from Michigan quickly pulling in fishing nets and scuttling back to its port. Evidently, U.S. fishermen had been poaching the site for years. Canadians avoided blowing the whistle, and even spread negative reports about catches from the shoal in an effort to steer others from the valuable fishing ground. Tragically, no one reported the menace to the shipping industry.

Efforts to blast the shoal away were ineffective, but it was accurately charted on navigation charts during WWII. Every captain sailing Lake Superior today gives wide berth to the mysterious graveyard of Superior Shoal.