Welcome to PB. What area of NE Ohio are you near?
I am about an hour north of you. North of Ravenna and the old arsenal. I had three guys qoute me, and didnt really like thier ideas of how to do it. One was ok, but the price was really high and I wasn't convinced it was because he was good. I now see another guy advertising in the farm bureua newsletter that claims to do ponds.
If you don't change the current outflow device (if there's a huge rain event, where does the water go once it is full?) you shouldn't have to worry about flooding anybody downstream.
I would tread carefully. Even if the outflow was the same, and someone down stream got flooded by an odd circumstance, they might come back at you and say it was because the pond was altered.... Better keep strict records of the past elevations, etc., for liabilty sake.
What about taking the dirt from making it deeper and using it to fill in the neighbors property, with thier permission of course. Make a mowing strip around it that's all on your property. Then the water wouldn't be on their property and you have sole rights to the water. They might be happy about not having a soggy backyard.
