The lowermost gage with a period of record greater than fifty years is at Hermann, Missouri – upstream of the mouth of the Missouri – where the average annual flow was from 1897 to 2010. About , or 98.7% of the watershed, lies above Hermann. The highest annual mean was in 1993, and the lowest was in 2006. Extremes of the flow vary even further. The largest discharge ever recorded was over on July 31, 1993, during a historic flood. The lowest, a mere – caused by the formation of an ice dam – was measured on December 23, 1963.