A small river dam is a structure built across a river to control the flow of water. It is often referred to as a WEIR, which is a four-letter word used to describe a low dam built across a river or stream. The purpose of a small river dam is to regulate the water level and flow rate of the river, as well as to provide a source of hydroelectric power. Small river dams can also be used to create recreational areas such as fishing ponds and swimming pools.