When a river flows into the ocean, what phenomenon occurs due to the slowing of the water?

When a river flows into the ocean and its speed decreases, the water loses the energy needed to carry sediment that it has been transporting. As the river's flow diminishes, sediment begins to settle out of the water, leading to the accumulation of materials. This process of sediment deposition can ultimately result in the formation of a delta, which is a landform that typically extends into the ocean.

Deltas are characterized by their triangular shape and are formed over time as layers of sediment build up at the river's mouth. This sediment can include sand, silt, and clay transported from upstream areas. The deposition occurs because the river water slows down significantly when it enters the larger body of relatively still ocean water, leading to a drop in the river's velocity and, consequently, its sediment-carrying capacity.

In contrast, other options like creating a lagoon or forming an estuary describe different processes. A lagoon is usually formed by a barrier that separates it from a larger body of water, whereas an estuary is a partially enclosed coastal waterbody where fresh and saltwater mix. The generation of a tidal wave is an unrelated phenomenon that involves the rise and fall of ocean levels caused by gravitational interactions and does not result from the transition of river water