Abstract Washington D.C. faces one of the highest 100‐year flood risks of any major city along the U.S. East Coast. In addition to storm‐surge inundation during hurricanes and nor’easters, water‐level observations for Washington are strongly skewed by major floods on the Potomac River. Using geologic and historic records we find new evidence for ice‐jam flooding at Georgetown during the Little Ice Age, as recently as 1784, that was up to ∼2x the magnitude of the largest events of the past hundred years (1936, 1942). Over the 19th century (a) human modifications to the Potomac estuary as well as (b) increasingly heavy rainfall and (c) land‐clearance in the watershed may have contributed to increasingly frequent large floods at Washington. Early surveys of the U.S. Capitol Building and other local landmarks also suggest sea level on the Potomac estuary at Washington has risen by upwards of 0.7 m (2.2 ft) since the 1790s.

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