Cpeaks, congrats on completing your pond. I'm not real educated but the biologist is(should be). I do know you are going to get things in your pond that you'd rather not have. Filling from a river will speed up your process but almost surely add some not so cool things. Bill Cody once showed me a drop of water under an electron microscope and I was amazed at the amount of life in one drop. My fear besides nasty fish, would be invasive plants and/or chemicals. I know EVERYONE is anxious to get their fish going asap but in 3-4 yrs if you do things correctly, you will be amazed at the results. That sounds like a lifetime but will flash by. The days are long but the yrs are short. I put 6 Koi in my pond and it took 5 yrs to get rid of em. One or two bad moves can set ya back quite a bit. I'd go with filling it and killing it off.
Just my personal opinion and others more experienced will probably chime in. Good luck which ever rout ya take.
Beware of Bill Ds 1 cent.

Do nature a favor, spay/neuter your pets and any weird friends or relatives.