Roy,

Please disregard my first reply - I skimmed your post and made an erroneous conclusion.

I read it as you were building a new "third" pond downstream of your large 3.5 acre pond. The 3.5 acre pond was the LMB/BG pond, and the new "third" pond was going to be the SMB/YP/RES pond. [That was my brain freeze.]

Moving on to your actual situation:

Like you, I would hate to poison out any "living" pond. However, the advice to eliminate any possible "invasive" fish from the upper pond seems very good to me.