Researchers have voiced concern over a falling otter population in the Thamirabarani River, caused by destruction of natural habitat. Also known as Tamraparni or Porunai, it is a rare perennial river flowing wholly within Tamil Nadu. It rises at Agastyarkoodam Peak in the Pothigai Hills of the Western Ghats and empties into the Gulf of Mannar after a course of about 128 km through Tirunelveli and Thoothukudi districts. Its tributaries include Gadananathi, Manimuthar and Pachaiyar, and dams include Papanasam, Karaiyar, Manimuthar and Servalar. The river hosts about 669 fish species and all three Indian otter species: Eurasian, Smooth-coated and Asian Small-clawed.