Presenter Holly Morris travels the Great Lakes, 94,000 square miles of fresh water that have shaped North American trade for centuries. The journey opens in Detroit, tracing the river's role in prohibition-era rum-running, then follows Michigan's coastline to Oscoda, where the lumber trade once moved by boat and earned the state its reputation as the source of green gold. Morris climbs 550 feet up the Mackinac Bridge for views across the straits where Lakes Michigan and Huron meet, then joins marine archaeologists searching Lake Superior's Shipwreck Coast, scanning murky water for the wrecks of ships lost to the lake. The film closes aboard a 1,014-foot freighter hauling 70,000 tonnes of Montana coal, where Morris spends three days with the crew learning what life on the water actually looks like for modern lake mariners. Part of a series on demanding boat journeys worldwide, this episode mixes history, industry, and shipwreck investigation into one route across America's inland seas.