The barbel zone is typically the first lowland (or middle) section of a river, but it can retain many of the characteristics of the upland grayling zone.
The barbel zone tends to have a gentle gradient with a moderate current, usually above 10 cm/s, and moderate temperature. Well oxygenated, it tends to flow over a mixed substrate of silt and gravel. Chub, dace and minnows from the grayling zone are usually present, but there is rarely sufficient oxygen for grayling to thrive. Other notable species beginning to appear in this zone include pike, perch, roach, rudd, eels and, of course, barbel. water, usually below 10 cm/s. Water temperature and oxygen concentrations are more variable than in the other zones, as it can be turbid and usually has a silty substrate.
The zone is typified by species such as bream, carp, tench and gudgeon, with pike, perch, roach and rudd from the barbel zone also present.