This grove just popped up in a thick patch right at the base of the dam. I thought it might mean something, I guess maybe not.
I agree that it MIGHT mean something.
Could be a small leak in the dam.
However, there should be "extra" water at the backside of the dam, solely due to the surface run-off from that slope.
Could even be as simple as the cottonwood seeds preferentially settling in the wind lee behind your dam.
Regardless of the actual reason, I would still cut and poison them. IF there is a small leak, those cottonwood roots will eventually expand the leak and pull water from your pond through their massive transpiration capability.
