Which of the following best describes a pool in a stream?

A pool in a stream is characterized by deep zones with low velocity. This description aligns well with the understanding of how pools are formed in stream environments. Pools typically occur as a result of variations in stream flow and riverbed topography, where sediment deposition can create depressions. These areas have slower water movement compared to adjacent riffles, which are faster-moving sections of the stream.

In pools, the reduced flow velocity allows for sediment to settle out of the water, leading to clearer water conditions which can support different aquatic life. The presence of deeper water in these zones provides habitats for fish and other aquatic organisms, contributing to the overall biodiversity of the stream ecosystem.

This understanding of pools as deep, low-velocity zones highlights their ecological importance and differentiation from other areas of the stream, such as riffles or runs, which do not share these characteristics.