The Johnstown Flood of 1889, the deadliest US dam failure ever, offers many lessons for geo-professionals. When the South Fork Dam was built in western Pennsylvania in the mid-19th century to facilitate transportation across the Commonwealth, its design and construction met the contemporary standard of care. However, decades later, a group of Pittsburgh tycoons hastily rehabilitated the dam to create an exclusive resort. While their dam repairs were shoddy, warnings of disaster went unheeded. On May 31, 1889, following a torrential rainstorm, the dam failed, flooding the prosperous steel town of Johnstown and killing over 2,200 people. After the disaster, outrage over the disaster and calls for justice were widespread. Yet the connections the tycoons had in the Pennsylvania legislature, the courts, and the press insulated them from the legal and financial fallout of the flood. The tycoons’ influence even compromised the ASCE investigation of the dam failure. Although society, the law, dam safety regulations, and engineering ethics have undergone many major positive changes since the disaster, the Johnstown Flood of 1889 stands as a stark reminder of the duties and responsibilities of civil engineers and particularly of geo-professionals.