If it's a safe area to fish at night, a large streamer or popper ought to tempt him. Although it's possible this fish has lived in this pool for years (esp if the pool is very deep or above a dam)....... I wouldn't bet on it. Bass populations in small streams like this are mostly transient and the odds of a bass reaching this size in such a stream are remote. More likely, this fish migrated into this pool and will migrate out sometime after Sept of this year. Or, there may be some local folks who have been artificially feeding him and that's why he's there and has grown so large(?).
Whatever the case, I think you've got a good chance of catching him - will be a fun pursuit.