Conemaugh Lake is three and one-half miles in length, one and one-quarter miles in width, and in some places one hundred feet in depth, located on a mountain three hundred feet above the level of Johnstown, its waters being held within bounds by a huge earth dam nearly one thousand feet long, ninety feet thick and one hundred and twenty feet in height, the top having a breadth of over twenty feet. It was once a reservoir and a feeder for the Pennsylvania Canal. It had been widened and deepened and was the property of the South Fork Fishing and Hunting Club, an organization of rich and influential citizens of Pittsburg. It was a constant menace to the residents of the Conemaugh Valley, but engineers of the Pennsylvania Railroad regularly inspected it once a month and pronounced it safe.
The club leased the lake in 1881 from the Pennsylvania Railroad Company. It paid no attention to the fears of the people of Johnstown, but merely quoted the opinions of experts to the effect that nothing short of an extraordinary convulsion of nature could affect the protecting dam.
Johnstown's geographical situation is one that renders it peculiarly liable to terrible loss of life in the event of such a casualty as that reported. It is a town built in a basin of the mountains and girt about by streams, all of which finally find their way into the Allegheny River, and thence into the Ohio. On one side of the town flows the Conemaugh River, a stream which during the dry periods of the summer drought can be readily crossed in many places by stepping from stone to stone, but which speedily becomes a raging mountain torrent, when swollen by the spring freshets or heavy summer rains.
On the other side of the town is the Stony Creek, which gathers up its own share of the mountain rains and whirls them along toward Pittsburg. The awful flood caused by the sudden outpouring of the contents of the reservoir, together with the torrents of rain that had already swollen these streams to triple their usual violence, is supposed to be the cause of the sudden submersion of Johnstown and the drowning of so many of its citizens. The water, unable to find its way rapidly enough through its usual channels, piled up in overwhelming masses, carrying before it everything that obstructed its onward rush upon the town.