Ahead of the holiday weekend, signs are posted at popular spots along the American River urging people to stay out of the water. Fast-moving water resulting from weeks of Sierra snowmelt is creating dangerously fast currents on the American River and many other waterways in Northern California. The flow of water through a river or a dam is reported in "cubic feet per second". Unless you know exactly what that means, it can be hard to grasp just what a "fast" flow looks and feels like. As of Wednesday, the flow from Nimbus Dam into the Lower American River is 15,000 cubic feet per second.