In order to investigate or remove obstructions from the channel or bed of any watercourse and thus prevent ice from gorging therein and to prevent flooding or pollution of such watercourse, the state water commission, any water resource district, any municipality, any board of county commissioners, and any federal agency authorized to construct works for prevention of damage by floods or for abatement of stream pollution, may enter upon lands lying adjacent to such watercourse to investigate or remove, or cause to be removed from the bed, channel, or banks of such watercourse obstructions which prevent or hinder the free flow of water or passage of ice therein. However, such entry upon adjacent lands must be by the most accessible route and the entering agency is responsible to the landowner for any damage.