Do you have any cavities or near cavities in the pond? If so, you may get CC reproduction. Some little CC might survive BG/LMB predation to add to their numbers. A possibility to consider.

"Where there' a willie, there's a way."
This Farming Life, BBC

"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
[Linked Image from i.pinimg.com]