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.
What is a Watershed? A watershed is the area of land that drains to a particular lake, river or other waterbody. The graphic above, from Michigan Sea Grant, shows how a typical watershed works. Imagine a raindrop falling anywhere inside that watershed; no matter where it lands, it will eventually find its way to the main body of water at the bottom. If it lands lands in another watershed, it will drain to a different waterbody.