Unusual formations have been found in many Martian craters resembling dams. Some geological explanations have been offered, in this paper many of these dams are examined. With many candidate artifacts such as in Cydonia, the Nefertiti formation, and in the KingÂs Valley found there may be an artificial explanation for these dams. Attempts are made here to falsify the natural explanation, to show they could not be formed by a geological process. Dams can occur naturally, a river for example might become silted up enough to block the water flow. Mud can also slump down in a crater to create a shape like a dam, then possibly catch water in it. However many of these dams have features hard to explain in this way.