Barbel are amongst the easiest fish to catch once you have located them. In midsummer, barbel are generally located in the most oxygenated areas, below weir pools for example.
Later on, they move out in seach of food.
If you are fishing small rivers such as the Ouse, or very clear rivers such as the Hampshire Avon, you can often locate them by sight.
On big rivers such as the Trent, this is virtually impossible, but there is one thing that most barbel love and that is underwater snags combined with a gravel bottom. The outside of bends and undercut banks also provide good barbel spots.
The best conditions to fish for barbel is during and immediately after a good flush of warm water produced by rain from the south west, especially in winter.
On many waters barbel do not like bright sunlight and your best chances of catching them are in the evening just after the direct rays of the sun have left the water, or at night.