An oxbow is a U-shaped bend in a river that looks like the curved wooden collar (often part of a yoke) that farmers once placed around an ox's neck to help it pull a plow or cart. When a river winds through flat land, it naturally curves back and forth in sweeping loops. Over many years, these curves can become so extreme that they nearly touch, forming a tight U-shape.

Eventually, the river might break through the narrow strip of land separating the two sides of the U, creating a shortcut. When this happens, the old curved section gets cut off from the main river, leaving behind a crescent-shaped lake called an oxbow lake. If you've ever seen an aerial photograph of a winding river with small curved lakes beside it, those lakes are old oxbows that used to be part of the river itself.