Lakes with the biggest 30-day level drops

2 of the 25 rows in this table tie on the ranked value: 2 at -3.64 (rank 23). Tied rows share a rank and are listed in no meaningful order.

Change = the latest daily water-level value minus the last value at or before the 30-day mark, for gauges conservatively name-matched to an assessed waterbody. A gauge that did not report on that exact day is compared against its nearest earlier reading, so the span can exceed 30 days. Spans differ across this table: 2 of 25 ranked gauges did not report on the day exactly 30 days before their latest reading, so their change is measured over 30 to 32 days. Rows are not strictly comparable where the spans differ. Levels come from USGS parameters that all report feet of water: lake or reservoir surface elevation (00062, 62614, 62615) and gage height (00065), measured from the gauge’s own zero. Each row names its measure. The elevations here are quoted against 2 different vertical datums (NGVD 29, NAVD 88), which do not share a zero, and one row reports a stage measured from a local project datum rather than from sea level, marked “local datum”. Absolute elevations are therefore not comparable between lakes. Change is measured within a single gauge, against its own baseline, so it compares a lake to itself and never one lake’s level to another’s. USGS does not file one daily statistic for every gauge: 8 of these 25 rows are a daily mean and the rest are a daily maximum or a reading at 08:00 or a reading at 24:00. A row's change, range and latest value are all that statistic's. Reservoir storage (acre-feet) is a volume, not a level, and is not ranked here. Gauges without both endpoints are excluded. Readings are daily-batch snapshots. 24 of the 25 readings ranked here are provisional and subject to revision by USGS. The cut falls inside a tie: the last row shown is at -3.09, and at least one further row matches that value exactly but falls outside this list. Which of them appears here is decided by the cut-off, not by the data.