America's Most Expensive River Was Built to Carry Nothing

America built a 30-mile river for $3.2 billion — and success means it never carries a drop. It sits empty in a North Dakota field, crossed by bridges over dry ground, waiting for the one week it's needed. Most people who drive past it have no idea what it is. Here's what it does, why it had to be built this way, and the part of the story the headlines skip.