A nested watershed is simply a watershed within a watershed. An example might be the Platte River watershed which is a nested watershed within the Missouri River watershed which in turn is nested within the Mississippi River watershed.

what watershed does everyone live on

it leads to the river tames

You can change a watershed by polluting it

Watershed liming is a type of way to get rid of Acid Mine Drainage (AMD). It is when you take ground agricultural limestone and spread it over all or part of a watershed. The limestone neutralizes the water that leaves the watershed so it will not infect other bodies of water. Rain, snow, etc. types of water react with limestone and move through soil, in result making it less acidic. The less acidic water will not leach aluminum from soil into close streams and will not make cases of acidic runoff. It also makes forest productivity and health better. : )

Source: Freshman Earth and Space Science class