River water deposits

The river water is said to be polluted with acidic wastes if the pH of river water is :

A river water is flowing at 5ms^-1 . The depth of river water is 10m. What is the shearing stress between horizontal layers of the river water? Viscosity of water is 1 mili decapoise.

Assertion (A) : It is easier to swim in sea water than in river water. Reason (R): Density of sea water is more than that of river water.

All the rivers ultimately drain into seas. However, river water is not saline while sea water is saline. Why?

Why is river water unfit for drinking?