The highly oxygenated water of a weirpool will attract good numbers of fish, even in polluted rivers, but if you want to catch these fish you need to know where in the pool to look.
Weirpools, with their distinctive smell of wet weed and wild plants, are almost always rich in fish. In semi-polluted rivers, they may be the only places sufficiently oxygenated (by the turbulent flow over the weir slopes) to attract good numbers.
Something for every species
For the same reason, fish also tend to congregate in these pools in spells of very hot weather, when oxygen levels are reduced elsewhere. They hold a wide variety of species because they combine, in a small area, fast, medium, slow, slack, deep and shallow water, gravel, sand and mud – an area for every species.
The thunder of falling water and the turbulence of the surface make it hard for fish to detect the vibrations of the angler’s tread, or to see him on the bank, so they are less readily alarmed than in the main river. It is well worth studying these pools and learning how to exploit them, even if it takes time. The rewards can often be very satisfying.
The currents in weirpools are complex and have to be understood if such areas are to be fished successfully. The simplest sort of weirpool can be thought of as circular with water coming over a sill at an entry point and running out over another sill. Pools with more than one feeding flow can be seen as several adjacent weirpools.
The simple weirpool, when the river is in good flow, will have a very fast current running down its centre usually broken up into turbulent white water. This very fast run of broken water is superficial. Only a few feet beneath it, the water is slow; still deeper, it is static, and at the bottom it actually flows in the opposite direction.
On each side of the fast, broken area, the water loops back in circular eddies with slack or still water in their centres, creating two horizontal eddies to right and left and the vertical eddy scouring the bed.
Fish head up-current; current brings them food and can be used to carry the angler’s bait down to them. There is no need to use a heavy ledger lead to crash through the broken water at the edge of the weir sill. A bait can be placed in the slow undertow on lightly leaded tackle and fed into the flank of the sill, where the back-current of a side eddy will carry it underneath.
All sorts of debris, including particles of food, are deposited in the heart of the two side eddies; and sometimes in the slacks where the diverging currents from these eddies hit the bank. Unfortunately, this debris includes anything from twigs to old prams and bicycle frames, although the centre of a weirpool eddy is a good spot to find fish – it is also ideal for losing tackle. It may cost you dear to explore each pool to discover which of them merits the expensive risk.
Fortunately, even where there is a lot of rubbish, fish prefer the cleaner bottom that runs round the centre of the eddy and may be found anywhere on or near it. Depending on depth, flow and variations in contour, it may be fished with either ledger, float tackle or a paternoster rig. In order to locate fish, whichever method is chosen, it is wise to let the bait move around the eddy, or to different spots around the circle.
Pay attention, too, to the run-out area of a weirpool. All the currents converge here, moving horizontally, vertically or at some angle in between. The bottom becomes shallower and the sides of the pool constrict the flow, so that drifting food items are concentrated into one area where fish feed without exertion. Big barbel, chub, roach, dace and grayling are often to be found on the gravel of the run-out. Bream and perch prefer the deeper water, though the perch often make forays into the shallows at dusk and dawn to catch small fry.
Trout also favour the run-out but, like pike, appear almost anywhere in weirpools. The species will often run right up the broken water at the centre in pursuit of small fish. In fact, small fish skipping down this white water may indicate the presence of a big trout.
Much depends upon the access to a weirpool. With some, a gentle slope permits fishing from the apron; if so, remember that it is usually very slippery and calls for nailed boots or waders. Some weirs, like Throop Mill, on the Dorset Stour, have a bridge from which it is possible to cast, but be sure in advance that you can get down to the poolside to land your fish. Access to sill or weir bridge is particularly important where there is more than one sill, or more than one sluicegate feeding the sill. This is because with two streams of broken water, there is usually an area of slack or slow water between them that almost always holds good fish. It may be impossible to fish this area except from above the sill. Otherwise, a position at the side of the weir is equally good and often allows tackle to be worked round the eddy.
Casting into smaller pools
In smaller pools, cast from the same place into the run-out when a change of tactics is indicated by fish leaping, breaking surface, or producing swirls on the shallows. It rarely pays to cast across the broken centre water to the eddy on the far side; the fast surface current acting on the far line will drag everything down to the tail of the pool and the run-out.