Paddle stretches of the St. Croix and you'll swear you're on a far-north wilderness river, yet this national treasure is practically in the backyard of the Twin Cities. With its wooded banks, pine-studded islands and sandstone and limestone bluffs, the St. Croix offers spectacular day paddles. Or bring your camping gear and make it a weekend. Many outfitters rent canoes, gear and shuttle service. Try St. Croix Falls, Wis., to Osceola, Wis., or Sunrise Landing to Wild River State Park. Stop at a sandbar for lunch and a swim.

Runner-up: Mississippi River