A dam according to the present disclosure includes a main dam including a first reservoir, and at least one first discharge part configured to discharge water stored in the first reservoir, an auxiliary dam spaced apart from the main dam at a predetermined interval and including a second reservoir configured to store the water discharged from the main dam, and at least one second discharge part configured to discharge the water stored in the second reservoir, and an underground water path being provided separately at a lower side of a bottom surface of the river or stream under a lower side of the second reservoir, and including a third discharge part.