Unless trying to back up a LOT of water, I see no reason here for any concrete. Essentially, what has been described as being wanted, is a Weir Pond, which is just a small dam in flowing stream bed that water constantly flows through, over and around.
The stream does not look to be down to bedrock, so driving 6-10" logs, side by side about 6-7 feet deep, and adding some rock in front to build a "ramp" for water to flow over will last through about any flow that wouldn't change the natural drainage course of the stream bed. If there is bedrock, some concrete/mortar using natural stone to build a 3-6 foot wide bridge/wall will be plenty also.
Bob did an article on Weir ponds...I'm not sure what issue, but here is a link to some of it. I had the pleasure of visiting this amazing place with Bob a couple years ago...
http://www.bobluskoutdoors.com/news-updates/building-a-pond-ron-morgans-system-2016-01-2490
