Question

River water is clear when sea water is not though both contain mud and sand

Answer 1

i think it is because river water is always moving and never stays in one place and it also deposits its solid particles such as mud and sand into sea or oceans but sea water is stationary and other rivers deposit mud and sand into the sea . 

Answer 2

The following are the reasons why the water of the river is clear when sea water is not though both carry mud and sand:

1. It is because the sea contains much of salt as contrasted to rivers.

2. River water as contrasted to seawater has more limited disturbance and mixing of water. Although, River water is moving it provides sufficient time for the process of sedimentation of silt and mud to the ground exterior to transpire. Accordingly, the above layers of the river water become clear.