High concentrations of visitors in a few protected areas (Royal Chitwan National Park, Annapurna Conservation Area, Sagarmatha National Park and Langtang National Park) have accelerated the degradation of the environment in these biologically fragile regions. Litter pollution is a particular problem in remote mountain areas and around mountaineering base camps. An often neglected factor is that porters and other support staff need fuel for cooking and warmth and usually have to resort to using firewood. However, tourism is a important revenue for Nepal and for the protected areas (45% of all tourists to Nepal visit one of the protected areas), and so a balance needs to be struck.