Analysis of water level elevations and discharges was performed for Pool 25 on the Upper Mississippi River as part of a study to increase ecological benefits of the operation of Lock and Dam 25. This dam was placed in operation in May 1939. Since that time, the operating plan for managing water levels has undergone several changes. Discharges for Pool 25 were estimated using data from the closest gaging stations, with corrections accounting for changes in watershed area. Discharge estimates since 1939 were used to compute exceedence frequencies on a weekly, monthly, and yearly basis. They were also used to calculate the percentage of time discharges were within specified ranges for the three time scales. Water level measurements at five in-pool stations were used to calculate the percentage of time water levels were above specific elevations for the same three time scales. Only data for the period between 1952 and 1993 were used for this part of the analysis because different water level management plans were in use before 1952. The results of this work, along with a companion study, show the expected frequencies when alternative water level plans may be utilized and the amount of habitat that would be affected by alternative plans.