If you go trekking you are required to register your intentions with the National Park, do so at their Information Centre San Martin 24 or (http://www.nahuelhuapi.go...)
fees/permits
At certain access points to the park you are required to pay the Park Entrance Fee of AR$50 May. 2011. This fee is payable if going to Pampa Linda Tronador and if entering the park on a boat excursion; there is also also a AR$11 port tax. Access to the refuges in the National Park around Bariloche are free: Refugio Frey, Refugio Lopez, Refugio San Martin & Refugio Italia.