This picture of the Nowitna River in Alaska shows two oxbow lakes – a short one at the bottom of the picture and a longer, more curved one at the middle-right. The picture also shows that a third oxbow lake is probably in the making: the isthmus or bank in the centre of the most prominent meander is very narrow – much narrower than the width of the river; eventually, the two sections of river on either side of an isthmus like that tend to break through and create a new, straighter course; a new river bank then starts to accumulate, sealing off the meander and leaving another oxbow lake.
An oxbow lake is a U-shaped lake or pool that forms when a wide meander of a river is cut off, creating a free-standing body of water. The word "oxbow" can also refer to a U-shaped bend in a river or stream, whether or not it is cut off from the main stream.[1][2] It takes its name from an oxbow which is part of a harness for oxen to pull a plough or cart.