It had been a cold, wet May and the ground in early June was saturated from three weeks of hard steady rains. Butte had already seen seven inches of rain and on June 6th  the temperature dropped and nine inches of snow fell on the city. As it melted, the soaked earth soon flooded.

A  century ago,  the Clark Fork and Blackfoot Rivers saw their greatest flood in recorded history. The rains and snow of 1908 sent torrents into the two rivers. By early June the Clark Fork River hit a record of nearly 17 and a half feet – a full 4 and a half feet above major flood stage. It wreaked havoc on western Montana. Residents along the river fled with the rise of the water. Bridges washed out. The high flows shut down the rail lines as tracks flooded or were buried in landslides, leaving thousands of passengers stranded. The mines in Butte, unable to ship ore by rail, were closed. 1908 was an election year as well, and the state’s Democratic Convention had to be postponed.

Along the Big Blackfoot River fears mounted over a log raft of some 50 million feet of lumber that was held behind the Bonner Dam. Just downstream, raging flows tested what was then called Clark’s Dam. Rumors abounded in Missoula about whether the new structure was about to give way.

Completed just six months earlier, the dam built by then Sen. William A Clark and was considered state-of-the-art. Into its construction went two million feet of timbers, 5000 barrels of cement, hundreds of tons of structural steel and untold thousands of tons of granite. The Missoulian reported that “No expense was spared in making the dam one of the strongest of its kind, and … enough power will be generated to furnish the entire western portion of the state with electricity for all purposes.”

Still the project engineers couldn’t have forseen the estimated the 48,000 cubic feet per second that gushed over the dam’s spillway in June of 1908. Clark’s workers reportedly attempted to dynamite the south side of the dam to relieve pressure but to no effect. The dam, nonetheless, according to one observer,  was “as solid as a rock,” The powerhouse, however, was flooded to a depth of ten feet, cutting off electricity for more than two weeks.

In the local press, Clark’s representatives steadfastly proclaimed the dam’s safety and bemoaned the circulation of rumors. “There is no more danger of the power dam going out,” said one of Clark’s officials, “than there is of the mountains washing down into the river.” Indeed he was correct about the dam holding, though it did require substantial rebuilding, but he proved quite wrong on the second assertion. Mountains along the Continental Divide, crushed and stripped of precious metals, did wash into the river as mine waste, strewing contamination from the headwaters of Silver Bow Creek on down the Clark Fork.

With those historic flows came the moment of origin of the Milltown Reservoir Superfund site, which stretches along 120 miles of river making it one of the largest in the nation. The great flood left more than 6.6 million cubic yards of waste, laden with heavy metals and arsenic, in the sediment behind the Dam. These toxic sediments poisoned the aquifer that was used by Milltown residents for generations before its designation as a Superfund site in 1983.

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