The Chub is in the main a river fish and can be found in most rivers in the country. Now days the trend is to have still water Chub. I would not be surprised if there is a new record set in the near future, the main reason I say this is because of the kinds of bait used on still water. Trout pellets and boilies are very high in protein and this will give the fish extra weight.
I still think that a Chub should be fished on the river, but that is because I am an old fuddy duddy. Chub are a hard fighting fish and can be caught on a variety of baits including bread, worms and good old maggots and those ever faithful caster.
Smaller Chub will be found in large shoals, but if you are after that 'big one' you will have to work harder and do some homework on the water you plan to fish.