The best fall colors occur during cranberry harvest, when marshes scattered throughout Wisconsin — and occasionally Minnesota — blaze a distinctive ruby red as countless mature berries float on the water’s surface. Cranberries grow on wiry, low-to-the-ground vines, and once the berries ripen, farmers flood the marshes because it’s the most efficient way to harvest them.

“The berries are full of air pockets, which make them buoyant, which makes them easier to harvest,” says John Stauner. He and his wife, Nora, cultivate nearly 200 acres of certified-organic cranberry vines at their James Lakes Farms near Rhinelander, Wis.

The tart berry is native to Wisconsin, flourishing in the region’s climate and soil; no wonder it was christened the state fruit in 2003. But there’s another reason the Badger State produces nearly two-thirds of the nation’s cranberries: government intervention. In 1867, legislation enabled growers to impound — or reserve — the water that’s vital for production.

The Stauners’ six-week harvest kicks off in early October. They supply several Twin Cities natural food co-ops, including Mississippi Market in St. Paul, Eastside Food Co-op and Linden Hills Co-op in Minneapolis, Valley Natural Foods in Burnsville and River Market Community Co-op in Stillwater, just in time for Thanksgiving’s annual cranberry relish-making ritual.