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On June 22, 1972, Hurricane Agnes dumped torrential rainfall on the region as it swept up the eastern seaboard from the Carolinas to New York, flooding the Potomac River and Rock Creek in the District.

According to a report by the National Weather Service, the rare flooding event hit D.C., Virginia, and Maryland after Agnes dumped 10 to 14 inches of rain. The Category 1 storm became one of the costliest natural disasters in U.S. history, totaling $2.1 billion in damages.

Rock Creek’s floodwaters spilled into the National Zoo, putting its shop, boiler room, and transportation buildings under 7 to 8 feet of water. A young wolf was the only animal that came close to drowning. In a heroic tale described on the zoo’s website, Theodore Reed, then the zoo’s director, successfully rescued the wolf by stripping off his clothes and jumping into the enclosure. The floodwaters at the zoo uprooted 173 trees. Waterfowl came within an inch of floating over the top of their enclosures.

Agnes created what geologists categorized as a flood occurring on average once in 85 years. James O’Connor, then a city geologist and associate professor of earth sciences at University of the District of Columbia, determined that even a 25-year flood would cause Rock Creek’s water level to rise 15 feet above the banks at the zoo’s southern entrance. A 100-year flood, he found in comparison, would cause it to rise 20 feet.

The zoo and Rock Creek Park were not the only places in D.C. to feel Agnes’ force. The Potomac River rose 15.5 feet at the foot of Wisconsin Avenue in Georgetown, creating the third-worst flood in 100 years, according to the National Weather Service.

The storm hit Virginia, Maryland, and Pennsylvania even harder. A total of 13 deaths and $126 million in damages were recorded in Virginia. Dulles International Airport recorded 11.88 inches in a 24-hour period. There were 19 deaths in Maryland and $110 million in damages. While flooding in D.C. proved less than devastating, two deaths occurred when a family went wading in Rock Creek and two children were swept away. The city also saw a fair amount of property damage.

A controversial interstate highway project at the time, the Three Sisters Bridge west of Georgetown, was finally wiped out by Agnes, according to accounts in 2006’s The Great Society Subway. Although anti-freeway activists had already stalled construction, the floodwaters washed away what had been built. The Washington Post wrote at the time that the bridge, which would have connected Arlington County to K Street NW via the Georgetown waterfront, “officially was killed for the third or fourth time yesterday. This time it looks unusually permanent.”

Metrorail construction was also delayed by the Agnes deluge.