Death due to disease is called death by natural causes. There are four main types of disease: pathogenic disease, deficiency disease, hereditary disease, and physiological disease. Diseases can also be classified as communicable and non-communicable disease.
A watershed is the area of land where all of the water that falls in it and drains off of it goes to a common outlet.
However, a watershed is more than just a piece of land that collects the rainwater and dumps it into the river. Anything that ends up in a watershed ends up in a body of water, including pollutants like discarded motor oil or paint, or sediments from trees cut down due to construction. These and other pollutants can contaminate a water supply, erode the land surrounding the body of water and disrupt aquatic habitats.