Monongahela's First Lock & Dam

Monongahela's First Lock and Dam. Three Rivers Heritage Trail. In 1841, a privately owned company called the Monongahela Navigation Company built the first navigation dam on the Monongahela River. This dam and Lock #1 became the first of 15 lock and dam complexes built on the Monongahela River by 1904. Lock #1 was once the nation's largest lock. , Before the locks were built, navigation was limited by sandbars, waterfalls, rapids and islands. Stabilizing the depth of the water for year-round boating was a great problem, and was not resolved until the system of locks and dams was completed. Dams raised the rivers water level enough to ensure that boat captains could navigate year-round. Locks moved boats around the dams. Through the locks came hundreds of boats and a constant stream of coal barges. By the early 20th century, boatmen called the Monongahela River the "little giant" because the stream carried more freight per mile than the Suez Canal and the Mississippi River. , The United Stated Army Corps of Engineers purchased the locks and dams in 1897. The Corps rebuilt the Lock and Dam #1 complex between 1905 and 1915. The locks and lock keeper's house stood on the opposite side of the river until 1936. In that year, the Emsworth Dam was completed and the river pool raised high enough to eliminate the need for a lock and dam on this site.