The best swims to try are those where the light is dim as perch feed best in these conditions, when their poorer-sighted prey are then at a disadvantage. For this reason, dull days are much to be preferred and if you can fish at dusk, or better still dawn, so much the better. Undercut banks especially around tree roots are particularly flavoured, provided that the current is sluggish. Such swims with a faster current will probably hold chub. Other likely areas are bridges, and bulrush beds.
Bulrushes are the tall round-stemmed reeds that look like green fishing rods.
They grow only on a firm bottom such as gravel or clay, which perch definitely seem to prefer. Unlike chub, which can sometimes be enticed out of such cover, the bigger perch tend to remain close to their sanctuary. To avoid getting snagged use a swan shot link leger, and if you want to add a float to fish above the bottom, attach it to the line at both ends with long pieces of valve rubber. If you put the shot directly under the float and cast underarm tight to the cover, you should find that the lighter bait follows the float and doesn't swing away from where the fish are holed up. Turning to baits, maggots in weedy water are a poor bet as you need heavy tackle which in turn means that small baits won't behave naturally.