Option 1: Pothole - A pothole is a small, deep hole that forms in the surface of a road or pavement due to wear and tear from constant traffic or weathering. It is not formed in the course of a river, so this is not the correct answer.

Option 2: Levee - A levee is an embankment or ridge of sediment that is built alongside a river to prevent flooding. It is not formed when an old meander is closed off by deposition, so this is not the correct answer.

Option 3: Oxbow lake - An oxbow lake is formed when a meander in a river is cut off from the main channel. Over time, the meander becomes isolated, and the water flow bypasses it. This results in the formation of a curved lake that resembles the shape of an ox`s bow. This is the correct answer.

Option 4: Flood plain - A flood plain is a flat area of land on both sides of a river that is prone to flooding. It is not formed when an old meander is closed off by deposition, so this is not the correct answer.

Therefore, the correct answer is option 3: Oxbow lake.