What is the characteristic feature of a retention basin?

A retention basin is primarily designed to hold water in a pool, which is a defining characteristic of its function. This feature allows the basin to capture and store stormwater runoff, thereby managing water flow and reducing the risk of flooding downstream. By retaining water, these basins also facilitate sedimentation and allow for pollutant removal through natural processes, which can improve water quality before it is released into the environment.

The other options describe features or functions that do not align with the primary purpose of a retention basin. For instance, while some basins may have recreational elements, such as hiking trails or viewing areas, the main function remains the temporary storage of water. Hence, the answer highlighting the retention of water in a pool accurately reflects the basin's critical role in stormwater management.