Rap·id, Rap·ids , n. The part of a river where the current moves with great swiftness, but without actual waterfall or cascade; sometimes called whitewater; -- usually used in the plural; as, the Lachine rapids in the St. Lawrence. For boaters on the river, it is a place that can be hazardous, with danger of capsizing or crashing into large rocks.
Row, brothers, row, the stream runs fast,
The rapids are near, and the daylight's past. --Moore.