What term refers to the land at the bottom of a river?

The term that refers to the land at the bottom of a river is "riverbed." The riverbed is the substrate or ground where the river flows, typically composed of various materials such as gravel, sand, silt, or rocks. This area is essential for the ecology of the river, providing a habitat for various aquatic species and influencing water flow and sediment transport.

In contrast, the riverbank refers to the land alongside the river's edges, which can be either steep or gradual depending on the landscape. Shoreline is a term generally used to describe the land along the edge of a body of water, such as a lake or sea, rather than a river. The term "bank" can refer to various landforms but is often used more generally to describe the sides of a river, not the bottom.