Floods have continued to be a concern for Johnstown , which had major flooding in 1894 , 1907 , 1924 , 1936 , and 1977 . The biggest flood of the first half of the 20th century was the St. Patrick 's Day Flood of March 1936 . It also reached Pittsburgh , where it was known as the Great Pittsburgh Flood of 1936 . Following the 1936 flood , the U.S. Army Corps of Engineers dredged the river within the city and built concrete river walls , creating a channel nearly 20 feet deep . Upon completion , the Corps proclaimed Johnstown " flood free . " The new river walls withstood Hurricane Agnes in 1972 , but on the night of July 19 , 1977 , a severe thunderstorm dropped 11 inches of rain in eight hours on the watershed above the city and the rivers began to rise . By dawn , the city was under water that reached as high as . Seven counties were declared a disaster area , suffering $ 200 million in property damage , and 78 people died . Forty were killed by the Laurel Run Dam failure . Another 50,000 were rendered homeless as a result of this " 100-year flood " . Markers on a corner of City Hall at 401 Main Street show the height of the crests of the 1889 , 1936 , and 1977 floods
Flood of March 1936
Johnstown flood of 1936
Johnstown Flood