Conflicts have arisen when commercial rafting operators, often in co-operation with municipalities and tourism associations, alter the riverbed by dredging and/or blasting in order to eliminate safety hazards or create more interesting whitewater features in the river. Environmentalists argue that this may have negative impacts to riparian and aquatic ecosystems, while proponents claim these measures are usually only temporary since a riverbed is naturally subject to permanent changes during large floods and other events. Another conflict involves the distribution of scarce river permits to either the do-it-yourself public or commercial rafting companies.[17]