I figured as much, my thought also that it came in with the RES as it is the only one we have caught. It is possible someone someone stocked the bass but I was pretty vocal to friends and neighbors about placing anything in the pond. Not likely anybody put 10+ <6" bass in the pond as Ohio has the 12" min in public waters but I guess you never know. I am leaning towards they came from upstream. A few reasons why:

1) Have not seen, hooked, or felt anything over ~6"
2) I was seeing my LCS up until a major rain event where ditches/streams were flooding over their banks. We had HEAVY runoff into the pond.
3) My understanding was LMB spawned in similar ways to BG/RES. The only beds I have seen are RES and we walked the pond almost daily all summer.
4) Prior to the major rain event we saw nothing swimming with the lateral stripe, minus the LCS which hung out in the same spot everyday. Few weeks after the rain event I saw some fish with the lateral black stripe cruising the banks. I assumed they were my LCS but were too deep to positively identify. Now I am relatively confident they were LMB. Have not seen the LCS since the rain.

Not ruling out a "friendly neighbor" but haven't seen anything pointing to it. The property is gated/fenced, surrounded by farm fields and has a lane that goes back 600 ft before the property opens up. Also put up signs to the effect of don't stock fish it is a managed pond. The farmer next door keeps a pretty watchful eye on the place and challenges anyone that he is not familiar with, he is a great neighbor. As said before it is possible so I need to put up a game camera as an extra added check.

I still need to attack the inflow problem as we could have this same issue next spring or even later this year. Temporarily I am going to place straw bales across the inflow to (hopefully) filter any incoming fish. Later this fall we are going to widen the pond ingress and level it off to slow the rate of flow. Going to design it similar to the emergency spillway. Looking at using Bill D's rock idea as a more permanent solution.

Caught another one this morning so the total stands at 12. Catches are starting to slow down a bit but it has been cold. What do you think the odds are we can catch every single bass in the pond this fall before the spawn in the spring? Thanks for the positive fish ID.