Why does a river commonly deposit sediment when it enters a lake or sea?

Correct answer: Water velocity and carrying capacity decrease

The correct answer is A. As a river reaches a lake or sea, its channel usually becomes less steep and its flow spreads over a much wider area. This causes velocity and carrying capacity to decrease. A slower current cannot keep as much sand, silt, clay, and gravel moving, so the sediment settles on the bed or near the river mouth. Continued deposition may produce a delta where conditions are suitable. B is wrong because gravity continues to act and helps particles settle. C is scientifically incorrect because sediment does not instantly become gas. D is wrong because the sea does not make the river flow uphill; the river still flows downslope toward the receiving water body. Memory cue: slower water drops its load.