Is it debris, is it a damsel, I’m not sure carp know either, but they slurp it up. I came up with this pattern after fishing a vegetation riddled pond with carp feeding in and on said vegetation. Enter the Wakame Salad. Wanting a fly that was enticing both on the the fall, and off the bottom, I chose rubber legs for the tail, and a soft lively dubbing (FTD Nymph Dubbing in Peacock) to create some movement and resistance. Light in weight, keeping it stealthy, and as previously mentioned, great on the fall or off the bottom.
Tip: when dry this fly is great on top until slowly sinking. That said, for using on the fall, wetting the fly first is a must. (it takes a few dunks and you're good)