The term 'River Block' is a combination of two words, 'DAM' and 'RIVER'. A DAM is a structure built across a river to control the flow of water. It is used to create reservoirs, generate hydroelectric power, and provide flood protection. The river block is the area of the river that is blocked off by the DAM. This can cause changes in the river's ecology, such as decreased water flow, increased sedimentation, and altered habitats for fish and other aquatic life.