To determine which portion of a stream is most likely to become an oxbow lake in the near future, we need to understand the process of oxbow lake formation.
An oxbow lake forms when a meandering river or stream erodes through the narrow neck of a meander bend, cutting off the meander loop and isolating it from the main channel. Over time, the isolated meander loop fills with sediment and water, forming an oxbow lake.
Based on this process, the portion of the stream that is most likely to become an oxbow lake in the near future is the neck of a meander bend, where erosion is occurring. As the river or stream continues to erode the neck, it increases the likelihood of the meander loop becoming completely cut off from the main channel.
Therefore, the narrowest point of a meander bend, where the stream is actively eroding the neck, is the most likely portion to become an oxbow lake in the near future.