when was the first one built?
1890
Black Eagle Dam
The first dam on the site, built and opened in 1890, was a timber-and-rock crib dam. 
what river forms the border between iowa and nebraska UNANSWERABLE which are the main tributaries of the missouri river? James, Big Sioux, Grand River systems etc. where does it originate from? It officially starts at the confluence of the Jefferson and Madison in Missouri Headwaters State Park near Three Forks, Montana. does it have any dam over it? Yes, Black Eagle Dam, Ryan Dam, Canyon Ferry Dam, etc.
wiki:5672275
Black Eagle Dam [SEP] Introduction
Black Eagle Dam is a hydroelectric gravity weir dam located on the Missouri River in the city of Great Falls, Montana. The first dam on the site, built and opened in 1890, was a timber-and-rock crib dam. This structure was the first hydroelectric dam built in Montana and the first built on the Missouri River. The dam helped give the city of Great Falls the nickname "The Electric City." A second dam, built of concrete in 1926 and opened in 1927, replaced the first dam, which was not removed and lies submerged in the reservoir. Almost unchanged since 1926, the dam is long and high, and its powerhouse contains three turbines capable of generating seven megawatts (MW) of power each.