Davidson River N.C.

Still considering building a home around Bevard, and with older knees would
plan on using the Davidson River as a easy place to spend a few hours
casting.
One small problem---much of the fishing on the Davidson is done with small
dry flies and midges..Shops sell lots of 22 and 24 size flies.
As these are all hatchery fish (raised two miles upstream ) why don't the
fish prefer bigger flies.? Feel sure they were raised on pellets.
Don't these fish know old indians have weak eyes.

Can anyone explain why this is a "midge stream".
JOE