Define "water pollution".

The introduction of a foreign substance, usually harmful, into a water source

Explanation:

Anything that doesn't naturally belong in the water

Examples: plastics, scrap metal, fertilizers

leaves, sticks, and cadavers are more of a grey area. They are part of nature but if it clogs the water source, drastically changes the ecosystem or are dumped there, then they are considered pollution.

Answer: It is the indiscriminate dumping of nonuseful substances into water bodies

Explanation:

Water pollution occurs when non-useful substances like chemical, industrial, human wastes etc, are dumped into water bodies (oceans, rivers, lakes) as a means of disposing such wastes

For instance: water pollution occurs when unused battery is drop in the lake, sewage is dumped in the river etc