A shoal of fish lying in the current and facing upstream do not have to move about a great deal to find food. The current brings the food to the fish which only have to move slightly to one side or upwards to intercept the food particle. If you feed the swim with loose maggots the fish pick them up as they are washed down in the current. When a bait is presented on or close to the river bed a fish feeding in this way will not pull the float under. What happens is that the fish snatches the bait and the float continues to travel down until the line tightens between the hook and the float and the force of the current pushes the float under. The faster and shallower the river you are fishing then the faster this happens. In deep rivers with a steady flow there is always a slight time lapse between the fish intercepting the bait and the float dragging under. When you are fishing over depth there is often no noticeable difference between a bite and the hook dragging on the riverbed, so if you are in any doubt always strike.
For ideal bait presentation in flowing rivers the rate at which the float is allowed to travel down the river should be a lot slower than the surface current. This is achieved by controlling the rate at which the line leaves the spool of your reel with your forefinger. The reason for doing this is that the surface water speed of a river is considerably faster than at the bottom. This is more noticeable in deep water than in the shallows. If, in a deep, swift river, you allowed the float to travel down at the same speed as the surface current the hookbait would be dragged far too quickly along the bottom. Many anglers mistakenly believe that when you slow down the rale at which the float travels down the swim, you are allowing the baited hook to travel down ahead of the float. This is not so, and all you are doing is allowing the bait to travel through the swim at the normal speed of the current near the river bed. The variation in speed of flow between the surface and the river bed is very marked, and in limes of extra water can often cause anglers to ignore a swim which is full of fish. Because they wrongly assume that the flow is equally fast on the bottom. You will often see pictures in books and magazines showing what happens when you hold your float back in the current, and most of them are wrong. The line will not form a forward curve towards the baited hook and the bail will not be waving enticingly under the noses of the waiting fish, as is so often stated. The line immediatelv below the float will billow forward in the fast current, but will curve backwards nearer the river bed where the bait is being dragged along in the much slower current.