Before revision: It can refer to a branch of a main river, which lies alongside it and then rejoins it, or to a body of water in a main river, backed up by the tide or by an obstruction such as a dam.Merriam Webster Dictionary
After revision: Manmade restrictions to natural stream flow or temporary natural obstructions such as ice jams, vegetation blockage, or flooding of a lower stream can create backwater.It can refer to a branch of a main river, which lies alongside it and then rejoins it, or to a body of water in a main river, backed up by the tide or by an obstruction such as a dam.Merriam Webster Dictionary