The pond is in his own yard not connected to anything...he can do what he wants with it.
I was going to suggest he do the same but only cause I figure he doesn't have the necessary eq't.
We had LDWF spot check ours (10 acres) once and they told us we had too much "trash" fish like mullets, etc. We ended up draining it and starting over.
Someone mentioned Rotenone (sp?). We used that in a corner where the dozer went deep to pick up the levee on the bottom. shite was amazing. Within seconds the fish were on their sides flapping. Not sure how it takes the H2O out of the water so fast but it works.