Sure, it’s tough to find a needle in a haystack. But just try locating someone’s lost treasure — a wedding band or beloved heirloom pendant — on the silty bottom of a lake in 60 feet of murky water.

ISLE ROYALE, MICH. – The Voyageur II ferry arrived on a foggy morning at this remote and rugged national park after a two-hour trip across the frigid waters of Lake Superior. A few dozen passengers ...