I have caught some of the biggest and hardest fighting smallmouth I’ve caught on this river I fish in southwest Ohio in a spot right alongside an old 1800s stone house that’s behind a bigger, nicer house from the same era. I’m guessing there was a mill there, I know this river had a lot of them. 

 

Did mills create deep holes or some sort of ideal structure that would explain why the bite is so strong there and the fish so big?

Yes it did create deep water behind and that lasted sometimes long after mill dams were removed, in my state where they are removing these dams to this day, some long abandoned, the stripers are making there way back upstream. Both mills and electric production produced a lot of dams on local waterways. Same principal as where small trout streams are blocked by beaver dams producing tiny 1-2 acre ponds that produce much larger trout. Smallmouth love these deeper water havens. 

2 hours ago, Tatsu Dave said:

Yes it did create deep water behind and that lasted sometimes long after mill dams were removed, in my state where they are removing these dams to this day, some long abandoned, the stripers are making there way back upstream. Both mills and electric production produced a lot of dams on local waterways. Same principal as where small trout streams are blocked by beaver dams producing tiny 1-2 acre ponds that produce much larger trout. Smallmouth love these deeper water havens. 

Awesome, yeah that’s what I figured. How cool is it that human activity from the 1800s produced monster fish? Why do they like this deeper water, cooler?

Cooler for sure and a place that for decades has always provided a small lake type ecosystem. More baitfish and deeper cover and ambush points for smallmouth to lay behind in the ever present current.  

They were a secret hotspot for over 5#ers when we were young and poor.

The 3 mile stretch of the creek I fish has 3 dams on, pretty much all that remains of the many mills that were on the creek in the early to mid 1800's.  They're not going to be torn down, historic structures, though a couple were damaged in the flooding after Hurricane Floyd back in 1998.  Over the years the areas immediately behind the dams has silted up still water but shallow.  The pools behind the dams run from about a 1/4 to 1/3 mile behind them and it's hard to reach parts of them.  They have some of the deepest water in the creek and if I'm not fishing the creek I walk on the path above it for exercise.  Over the years I've seen some big bass, 3-5 lb range, both smallmouth and largemouth, in those pools.  A couple of pictures of the dams.  The first is a long shot looking upstream at one of the dams and a close up of the pool below it.    The second set is one of the larger dams, and then the back end of the pool, about 1/3 of a mile upstream.

It is common for a deep hole to exist near a dam, spillway, mill, or similar manmade structure. These deep holes can be very good places to fish since predatory fish often congregate in these places.