Before the construction of today's modern locks and dams, thousands of long, narrow barriers were built out of rock and mats of brush. Sticking out from the shore, (and not going all the way across the river), these wing dams narrowed the channel and increased the current, which inhibited  sediment from collecting in the main channel.  

According to the caption on a huge poster of this image in the Jefferson County -"Oh-we-wouldn't-have-any-Trimble-County"-Historical Society in Madison, the dam is still in place, but was submerged with the activation of the McAlpine Dam in 1929