Pennsylvania's streams have frequently flooded. According to William H. Shank, the Native Americans of Pennsylvania warned white settlers that great floods occurred on the Delaware and Susquehanna rivers every 14 years. Shank tested this idea by tabulating the highest floods on record at key points throughout the state over a 200-year period and found that a major flood had occurred, on average, once every 25 years between 1784 and 1972. Big floods recorded at Harrisburg, on the main stem of the Susquehanna about downstream from Lock Haven, occurred in 1784, 1865, 1889, 1894, 1902, 1936, and 1972. Readings from the Williamsport stream gauge, below Lock Haven on the West Branch of the Susquehanna, showed major flooding between 1889 and 1972 in the same years as the Harrisburg station; in addition, a large flood occurred on the West Branch at Williamsport in 1946. Estimated flood-crest readings between 1847 and 1979—based on data from the National Weather Service flood gauge at Lock Haven—show that flooding likely occurred in the city 19 times in 132 years. The biggest flood occurred on March 18, 1936, when the river crested at , which was about above the flood stage of .