One other possible option. Does the stream run all year?
If it does, this might be an option. Simply dump a number of loads of large rip-rap ahead of the existing dam to back up a pool behind it.
When I was a kid, a bunch of us did this in Cow Creek (much larger than the stream you have). Below this overflow county bridge the water did not get deep enough to maintain fishing. There were lots of rocks in the creek. So by hand my brothers and a bunch of neighbor kids picked up and dug rocks from the bottom of the creek and surrounding area and created a "dam" a ways below this overflow type concrete bridge. We were able to back up enough water to pool below the bridge that it could be fished. We never tried to dam up all the water, just to back the flow up enough to create a deeper pool.
If your water flows year round, you could possible just pile lots of rip-rap, letting the natural process of clogging up, and let the water flow through the "dam" but in the process backing water up several feed deep. If this is done, you need big enough rocks so the water can't move them downstream. We are talking minimum foot in diameter and 18' better. Make sure water runs over the rocks and not around, or you just create a new creek channel to one side.
I don't expect you to adopt this method. Just giving you some ideas for your thought process.
