On March 12, 2004, the Big Bay Lake dam failed, releasing water and affecting lives and property downstream in southern Mississippi. The dam is located near Purvis, Mississippi, on Bay Creek, which flows into Lower Little Creek about 1.9 miles downstream from the dam. Lower Little Creek flows into Pearl River about 16.9 miles downstream from the dam. Knowledge of the hydrology and hydraulics of floods caused by dam breaks is essential to the design of dams. A better understanding of the risks associated with possible dam failures may help limit the loss of life and property that often occurs downstream of a dam failure. The USGS recovered flood marks at the one crossing of Bay Creek and eight crossings of Lower Little Creek. Additional flood marks were also flagged at three other bridges crossing tributaries where backwater occurred. Flood marks were recovered throughout the stream reach of about 3/4 to 15 miles downstream of the dam. Flood marks that were flagged will be surveyed so that a flood profile can be documented downstream of the Big Bay Lake dam failure. Peak discharges are also to be estimated where possible. News reports stated that the peak discharge at the dam was about 67,000 cubic feet per second. Preliminary data suggest the peak discharge from the dam failure attenuated to about 13,000 cubic feet per second at Lower Little Creek at State Highway 43, about 15 miles downstream of the dam.