Every person owning or occupying property through which a watercourse passes shall keep and maintain that part of the watercourse within the property free of trash, debris, excessive vegetation, and other substances that would pollute or contaminate the flow of water. In addition, the owner or lessee shall maintain existing privately owned structures within or adjacent to a watercourse, so that such structures will not become a hazard to the use, function, or physical integrity of the watercourse.