If you ever get the chance to examine a gravel pit that has been drained down have a good look at the shape of any features. Unlike the text books, they will not be of even width, length, depth, or even composition. There will be areas which might attract fish more strongly than others. Although there are a whole host of things to look out for when plumbing up, some of the most consistently effective spots are where there are very slight differences in the depth.

Take your average tench for example. If a tench wants to move from one side of a bar to the other it has two options. It can either swim around the bar, which may be some considerable distance, or it can risk going over the top. Now for a big fish, the latter option may not present a great risk, but the remnants of the behaviour of the younger fish mean that it will still be less willing to move over shallow water, for fear of being eaten. The tench will automatically head for the spot where the water over the bar is deepest. This may only be a difference of a few centimetres, but even this small difference is enough to give the fish more confidence. Although fish moving over bars are not always feeding, I would be quite happy to put one bait in the slight depression on top of the bar and feel that I was in the best position to catch any fish inclined to get to the other side.

Another example of where slight difference in depth can make a huge difference is when fishing the margins. Now, most people approach margin swims by plumbing away from the bank in a straight line. This tells you where the ledge is and the various depths, but how does this compare with the depth to the left and right, and in other areas of the margin? For predators in particular we have found that the areas where the marginal slope is slightly steeper than the surrounding area are definite hot spots.

If you visualise how a pike stalks its prey, these deeper valleys allow the pike to move up the marginal shelf towards its prey without being seen until the last second. The slightly deeper water acts as cover from which the predator can launch an attack. These marginal hot-spots are surprisingly common. Often they will be formed where the drag line stood on the bank when the lake was being dug as the bucket cut into the base of the bank. They can also be found when water has been pumped into the lake for a while. Differences in the lake bed can also, over time, lead to erosion at different rates, which again can lead to depressions being formed.

Finally, there are the slight depressions found in apparently open water. Again, these areas are particularly attractive to pike, with as little as 10 centimetres marking the difference between success and failure. Such spots are amongst the most difficult to find, but get into the habit of measuring the depth accurately at regular intervals and you will find these features. Alternatively, an approach I use a lot in the winter months, is to fish with four rods (where allowed) and to keep the baits on the move. This very active form of predator fishing covers a lot of water and allows hot spots to be found by trial and error. By exploring the lake bed after a fish has been caught, features can become apparent that might otherwise have been dismissed as being irrelevant. I suppose the take home message is, to recognise that even subtle differences in lakes and rivers can make a huge difference. Learn to map waters accurately and you will be surprised how quickly you learn the behaviour of the fish.