The sign at the waterfall says, "below the pool there is a dam for the Ukanc power plant, which was built during the construction of the Bohinj railway tunnel."
The Bohinj railway tunnel was built in 1909, so one can infer that this was built shortly beofre then.
Local Tourism website at (
visit link) tells us:
The Savica runs over 38 m long level and falls almost 51 m deep. Total difference in height is 78 m. Another smaller waterfall also falls 25 m deep. Both waterfalls together form the two-part waterfall in the shape of the letter A. Right after the pool, which is artificially supported, is a small dam.