Ecotourism is not without its drawbacks. Observers in Costa Rica, for example, have noted that although some national parks are large, most visitors want to see specific sites, which leads to overcrowding, trail erosion, and pollution at those sites. Also, scientists have noted changes in the behavioral patterns of local wildlife that appear to be linked to human activity. In Africa, the proximity of ecotourist groups to mountain gorillas puts the great apes at risk from human infectious diseases such as measles, polio, influenza, and tuberculosis.
Growth in ecotourism also promotes development outside protected areas, with attendant environmental degradation. In addition, not all of the people who participate in ecotourism activities have a deep understanding of the no-impact philosophy and a full appreciation of its importance; some of these people contribute to negative impacts through their actions in sensitive areas.