A part of a river where the water does not flow. (Cambridge Dictionary)
A place that does not change because it is not influenced by new ideas or events that happen in other places. (Cambridge Dictionary)
Water backed up in its course by an obstruction, an opposing current, or the tide. (Merriam – Webster)
A body of water (such as an inlet or tributary) that is out of the main current of a larger body. (Merriam – Webster)
A backwater is a place that is isolated. (Collins Dictionary)
If you refer to a place or institution as a backwater, you think it is not developing properly because it is isolated from ideas and events in other places and institutions. (Collins Dictionary)
A part of a river not reached by the current, where the water is stagnant. (Oxford Dictionaries)
Backwater – Wikipedia.
Along the backwater.