More Warmwater Fishing

I stopped for an hour the other day at a good looking hole at the outfall of a culvert. The stream is a warmwater trib of the Cannon that is mostly lakewater for much of the year. In the hole I could make out hundreds of bullheads of varying sizes.
I threw on a nymph from the carp swap and let it drift around... they weren't too active but if the drift was just right they took it - got two fair and one foul hooked. The bullheads were caught in a back eddy... I tossed the rig in the main flow on the other side of the pool and caught this common shiner. The entire pool was only about 15 feet across and about 20 feet long - not sure just how deep at plunge point. Anyway, as I was fishing, I saw a nice big carp hover from the dark depths to the edge of the hole - right in front of me... pretty cool. I tried a few carp nymphs with indicator - only so many places he could be sitting - but I couldn't hook him.