A person or scientist who studies on water is called as Hydrologist. Since the study of water and its properties is known as Hydrology, the persons who deals with this field are known as Hydrologists.
Geographer :
A scientist who studies Earth's natural environment and how human society uses the natural environment.
Herpetologist :
A person who studies reptiles and amphibians.
Archeologist :
Someone who studies people and what they did in the past from the things they left behind.
