If you watched Gold Rush Dirt last night, you might have seen reference in one of text info blocks to the Yukon Ditch. Here's a link to a 22 page report on the Yukon Ditch.
http://yukondigitallibrary.ca/Publicati ... 0Ditch.pdf
It was built in 1909 and took a year to complete. It was quite an engineering feat considering the location and where all of the material had to come from. Toward the end it mentions the dredges running then.
Leonard