I was just thinking about your pond beyond the pond. Could a carp
just swim away to the stream? Is the stream inviting/ If so, you
might lose it to better feeding grounds. They grow prodigiously.
Ours moved from 8' to 2.5' in a year and will level out at 3-4 ft.
Max eating is during growth, but they do fine regardless. i suspect
that if your pond exit is mall and the carp gets big, it will prefer
your pond to a stream. I am sure your county agent will have an
opinion about the duckweed and the grass carp.

Jim