Popular hill stations are at Ponmudi, Wayanad, Wagamon, Munnar, Peermade, Ramakkalmedu, Arimbra, Paithalmala of Kannur district, Kodikuthimala, and Nelliampathi.[176] Munnar is 4,500 feet above sea level and is known for tea plantations, and a variety of flora and fauna.[177] Kerala's ecotourism destinations include 12 wildlife sanctuaries and two national parks: Periyar Tiger Reserve, Parambikulam Wildlife Sanctuary, Chinnar Wildlife Sanctuary, Thattekad Bird Sanctuary, Wayanad Wildlife Sanctuary, Kadalundi Bird Sanctuary, Karimpuzha Wildlife Sanctuary, Muthanga Wildlife Sanctuary, Aralam Wildlife Sanctuary, Eravikulam National Park, and Silent Valley National Park are the most popular among them.[178] The Kerala backwaters are an extensive network of interlocking rivers (41 west-flowing rivers), lakes, and canals that centre around Alleppey, Kumarakom, Ponnani, Nileshwaram, and Punnamada (where the annual Nehru Trophy Boat Race is held in August), Pathiramanal a small island in Muhamma.