PROBLEM TO BE SOLVED: To solve a problem of a conventional agriculture robot system in which great human effort is required for water management of a rice field.SOLUTION: A marker water gauge 100 includes a main body unit 110 having, on its surface, main body surface regions 112-114 divided in the height direction. Each of the main body surface regions 112-114 entirely or partially exhibits a different color depending on whether it is in contact with water. The main body surface regions 112-114 exhibit the same color when they are in contact with water. The main body surface regions 112-114 exhibit mutually different colors when they are not in contact with water.SELECTED DRAWING: Figure 2
