The only river anglers I see 95% of the time in Yorkshire- Ouse , Swale, Ure and Derwent - are barbel anglers. Some take strength in numbers and set up their bivvies and tripods 5 metres apart ... The side effect is that I rarely see another angler on waters not rated for barbel and/or involving a walk of more than 5-10 minutes .
Large masses exert gravitational pull, so I guess all that lead they carry draws them together. There are crowd scene hotspots down here too, particularly where day ticket access plus night fishing allowed lets travelling visitors get a crack at the barbel. But there are plenty of anglers out for other species, and miles of empty bank for those who prefer that. For every Trent stretch densely packed with carbellers, there are numerous stretches on the larger tribs - Derwent, Dove, Soar - which used to be popular for barbel before the fishing dwindled to slim pickings. Even on the Trent, which is always "on fire" in the Angling Times, there are miles and miles of water where catching a barbel is a very long shot.