Which of the following is a nonpoint source of water pollution

"Rainwater pouring from an eroded bank into a river" is a non-point source of water pollution.

Explanation:

Bank erosion is the washing away of stream or river banks. This is distinct from erosion of the watercourse bed, known as scour. These erosion undermines the roots of trees which develop by a lake. As the roots closely connect the soil, they form abutments that jut out above the surface.

Non-point source water contamination is induced by widespread and isolated waste sources such as rain and snowmelt runoff, spills, leaks, and sediment erosions. To release any pollutant, without a permit, from a point source into navigable waters is illegal according to the Clean Water Act.