I live in Fairfax County - maybe 20 miles airline from my house to the center of DC, so I’m well acquainted with Washington summers.
Yup —Washington DC was built on a drained swamp. Reason congress always recessed in August was to escape the ravages of Yellow Fever.
Swamp.....seems apropos.....
DC and St. Louis are tied in my book for the worst combination of cold winters and hot/humid summers.