These rivers normally have their beginning, or source, high up in the hills and mountains. They derive their name from the fact that rain very quickly affects their flow; spate being the name for a sudden flood of water. Mountains and hills have more rainfall than the valleys, and consequently the lower reaches of a spate river can suddenly rise and flood when there has been no local rainfall. Because they are subject to sudden rises in level, spate rivers are probably the most difficult of all rivers to fish. The weather therefore plays an important part when fishing spate rivers not just the local weather, but the weather in the hills where the river starts.
The tiny trickle of water which forms the beginning of a spate river quickly gains momentum as it flows down the hillside. The bed of the stream is rocky and the water is sometimes stained from peat deposits or iron. Numerous springs and small streams join the main flow so that as soon as the lower slopes of the hills are reached, the size of the river has increased considerably. The river bed will still be boulder strewn but in the deeper pools there will be patches of fine gravel. In these reaches small trout will thrive, keeping under cover of large rocks during the low water levels of summer, and venturing out to feed at dusk and in times of extra water. As the river widens trout become more numerous and grayling appear. The river can vary a great deal in this region, between long shallow glides and narrow rapids. The banks are usually boulder strewn and in hot summer weather the river can be reduced to a trickle between the rocks. Plenty of smaller fish such as bullheads, stone loach and minnows thrive in this region. Crayfish, which look like tiny lobsters, hide away under the rocks. Where they exist, grayling can be found in large numbers and offer good sport right through the winter months.
After heavy rainfall the river can rise very quickly to form a brown swirling torrent. When fishing the upper reaches of a spate river after recent rain, always be prepared for the river to rise. Take care about crossing on to islands as it is possible for the river to rise before you have time to get back to the bank. In times of spate the fish will congregate in the quieter water near the bank, away from the rushing torrent. Very little weed manages to grow in the upper reaches of a spate river because there-is no silt in which the plants can anchor their roots. Insect life is restricted to those species of fly whose larvae or nymphs live under the rocks and stones. The nymphs tend to have flattened bodies so they can withstand the fast flowing water, and are of great importance to the fly angler stretches but at spawning time roach will often venture into the shallow, fast water. The nature of the river bed alters, and the gravel is replaced in the slower areas by hard clay or silt. Weed becomes more abundant and the river looks altogether more luxuriant. The river bankings be-come clearly defined and are often lined with overhanging willow and alder trees. Pike can be found in the deeper pools and although they may not be numerous they can grow very large. The river is still subject to as they are the main food supply of the trout and grayling.
The first coarse fish to appear along a spate river are dace and chub. Both these species thrive in fast flowing water, especially the dace. Chub become more numerous when the river broadens out into a series of deeper pools. Barbel can also be found as far as the upper reaches of a spate river. The upper limit of barbel is largely governed by the nature of the river bed. Although these fish thrive in fast, well oxygenated water, they prefer a river bed of fine gravel rather than rocks and boulders.
The middle reach ol a spate river is a mixture of fast shallows and deeper, willow lined glides. Trout and grayling can still be found in the faster stretches of river, but coarse fish begin to predominate.
Roach and perch can be found in the deeper spates but the effect of heavy rain is not quite so immediate or drastic as it is in the upper reaches. The first signs of an impending rise in level is a layer of dust forming on the surface in the margins. The flow gradually begins to quicken and a few twigs and leaves start floating down. If you notice any of these signs do not leave your tackle unattended or you may return to find the level has risen to swamp your belongings. It is often suggested that a spate river provides the best fishing when the level is rising, but in my experience this is not so. The initial surge of extra water brings clown a lot of debris and rubbish which, at times, can make fishing impossible. Once this rubbish has been washed away and the level begins to fall again the fishing will improve, especially if the river has been low for several weeks because of dry weather.
Several minor rivers may flow into the main river so that by the time it reaches the flat plains it has swollen to a considerable width. Over the centuries man has played a major part in altering the lower reaches of spate rivers. Because of serious flooding the banks have been built up to confine rivers to their courses.
Modern drainage schemes have included the removal of banksidc bushes so that the flow of the water is not slowed down. Very often these rivers are navigable in the lower reaches and boat traffic can seriously interfere with angling. The regular spates of these rivers carries down a great deal of suspended silt and sand in the water which settles on the bottom once the river slows down. This deposit of silt gradually builds up to reduce the depth, so on navigable waterways it is dredged up to keep the channel deep enough for boats. Because of this depth, any weed is confined largely to the margins of the river.
Thus, a stretch of river which is dredged and where any bankside vegetation has been removed is rather featureless and it is not at all easy to determine the likely fish holding areas. Where they exist, wcirpools and rougher water immediately downstream are obvious fish holding areas. Barbel and chub will often live right under the weir sill, below the white water. In sum-mer even bream will venture into the weirpools where the water is fast and turbulent. Trout are seldom encountered in these lower reaches but a few do manage to thrive in the weirpools. Wcirpools can be very dangerous places to fish so never take any unnecessary risks to reach a fishing spot. Even when very little water is flowing over the weir sill, green slime and algae can make it very slippery to venture across in lubber boots. Other obvious fish holding areas are where small rivers or streams join the main river, and during floods fish will congregate in these areas.