© Shutterstock-Rostislav Stefanek The tench is a common European freshwater fish The tench is a common European freshwater fish that has been introduced to much of the world. Although it is native to the lakes and lowland rivers of Europe and parts of Asia, the tench has become an invasive species throughout North America. The tench was introduced by humans to every continent on earth besides Antarctica as a sport and food fish. They are most often found in still waters with clay or muddy bottoms and abundant vegetation and can tolerate waterways with significantly low oxygen levels. Tench, also known as doctor fish, are thick, heavy, large-growing fish with an olive green to black back and bronze underbelly and a carp-like shape. Due to its tiny scales, this fish feels slimy when handled. Tench use small barbels that protrude from either side of its mouth to search for food along the river or lake bottom. Check out the dive site map below to see where tench have been sighted while diving.