The combination of Northerly winds, high pressure and a full moon means the temperature has plummeted to such an extent that I had the first frost of the Winter on my unhooking mat last night. As you might expect, after weeks of good weather the sudden cold snap has really dulled the fish's appetite. Even the small bait fish were difficult to tempt, how different from the day before when it was a bite a chuck fishing single maggot only a couple of feet below the surface.

What is interesting is that the actual water conditions were virtually identical on both days. The water temperature had only fallen by around a degree, yet the fish were obviously aware that this was the start of Winter proper. As water temperatures fall, fish eat less, but they still must eat and if you fish the right venues then you can keep on catching. Looking at the weather is often not going to tell you what is happening in your local fisheries. Different water bodies react differently to changes in the weather, remembering a few simple rules will help you decide which to fish on any given day.

Fishing a few different venues over the last couple of days provided an excellent example of how the weather effects different water bodies. As I have already mentioned, the small, relatively shallow reservoir that I have been fishing for perch stopped producing within a few hours. In such a small water body it only takes a very short time for the water temperature to begin to fall and the fish, with nowhere to hide from the cold, stop feeding.

At the other extreme, the large fenland river that I fished through the evening and night was still maintaining it's temperature and, as yet, the cold weather has had little effect. The difference between the two was very visible. Whilst the reservoir was almost life-less, the river was still dimpled by fish, both small and a few much larger. The fish were obviously still feeding as a nice fourteen pound pike just as the moon was coming up and a couple of two pound eels proved. The fish were actually steaming and warm to the touch, the difference in temperature was that marked. Although the river is no more than about five feet deep and only thirty metres across it's volume is very much larger than that of the small reservoir. Another important factor is that the river is inter-linked with the reed beds along its length and also the gravel aquifer. All of this buffers the variations in temperature experienced by the river, keeping it fishing for several days longer than the enclosed reservoir.

The effect of the environment can be most clearly seen in chalk streams. Although these are only small bodies of water and should cool rapidly, because their water comes almost solely from the aquifier there is a huge buffering effect that keeps the water cool in Summer and warm in Winter. In fact, chalk streams operate within a very narrow temperature range through the year and will produce even in extreme conditions.

Somewhere between the two extremes are large lakes and reservoirs. Their much larger volume means that the water will take longer to chill and so again, the fishing will continue to be good for a few days after a change for the worst in the weather. What has much more effect on large lakes though is wind-chill. Rather than the direct cooling effect of the air temperature, a cool wind will greatly increase the rate at which the temperature falls. Often when there is a strong cold wind on a large stillwater it is possible to find a difference in temperature of a few degrees between the windward shore and the banks behind the wind. Under these conditions I will always fish with the wind off my back.

Obviously, if different venues cool at different rates then they will also warm up differently. In general, big bodies of water will be the slowest to warm up, but this isn't always the case. One set of conditions that can produce good fishing in Winter is a spell of reasonably warm weather with high pressure and sunny days. Under these conditions, shallow lakes can warm up massively through the day, not because of the air temperature, but because of the warming effect of the sun. Such conditions can be very productive and can mean that even large lakes, if they are very shallow, can provide good sport. Even deeper fisheries can produce well during sunny high pressure conditions. Seek out shallow bays and other areas that act as sun traps and you will find elevated water temperatures.

Learning the effect of the weather on your local fisheries can save a lot of blank trips in Winter. Timing is everything in Winter. Go for venues that are either experiencing rising temperatures, or which have only limited falls for consistent sport even during the worst Winter chills. Whatever the weather, by learning about the changing moods of your local fisheries it is possible to keep on catching whatever the weather.