Reeds or whatever they breed in and around on the shallower flats. It's recon if not breeding time. Have found mid morning to mid afternoon to be best. If they're only in recon mode they'll come up from the depths for awhile and drift back down on and off all day. If you can find their route in and out from the depths you can be at it constantly. Could be a cut/trough, bottom weed line edge or type of bottom change, but look for the standing whatever to start finding them. On the odd chance they're actually up breeding I tend to let them be, I fish fairly small waters. Yet sight fishing is a blast and be quiet, they tend to be spooky, Northerns aren't that far away from breeding either and they check shallow also