Trout bums.

Every year I spend a couple of days in the Yorkshire Dales with my brother Alex. We sleep in his camper van, fish, hike and fish again all day, then spend the evening in the Farmers' Arms at Muker.

The weather is a bit of a gamble; too dry and the rivers shrink to a series of puddles, but after only a day of heavy rain, they become a life-threatening spate of brown water containing boulders that you can hear banging along the bottom, despite the white noise-like roar of the torrent. The sound is like the bowling alley from hell, with the M1 motorway in the background. 'Not conducive to a good night's sleep, as you expect your caravan or tent to be washed away at any minute.

Despite following the BBC weather page closely for days in advance, I had no idea what to expect. It could be floods or it could be drought. The problem for forecasters is that the High Pennines make their own weather that changes by the minute, whereas the nearby lowlands tend to stick to the general forecast. It can be a perfect day for the whole of northern England, but there will be a big, wet, black cloud over Shunner Fell filling the little "gutters" on the moors with white froth. The peaty water percolates into caves in the limestone and then gushes out into the upland becks that feed the main rivers of the Dales. Our river, the Swale, is the northernmost in Yorkshire (the Tees is in the next county), then in Wensleydale you have the

Ure, then the Wharfe, the Aire and the Calder. All are good trout rivers while they are in the hills, but grayling and then coarse fish predominate as you move downstream.

Alex and I are what an American would call "trout bums". Our favourite way to fish is by wading upstream waving a little fly rod. Trout are our favourite quarry and dry fly is our favoured method. It quite often involves falling in and this explains my brother's change of clothes midway through day two. On day three, he fell over a rock, then fell down, so he got the full set, in, down and over. (How are the bruises, Alex?)

To keep a fly dry, you have to coat it with gunk and wave it about in the air a lot. It's very good exercise and a good way to learn tree recognition. You catch a lot of trees. Think of doing this on slippery rocks while waist deep in white water and you will understand how easy it is to fall in.

The dry fly has to float on the surface and drift downstream unhindered, just like a real fly. The Swale is the fastest river in England, because it drops very rapidly over its first 20 miles. Your fly heads towards the sea at high speed, and you can't go after it, so you chuck it upstream and watch the line come back to you before you cast again. The line tends to drag in the current and pulls the fly after it, so it slips and skids across the surface only seconds after you plop it down. The trout (if he was there in the first place) usually bolts in panic at the site of your apparatus. In a pool he may bolt upstream, but in rapids he will usually get help from the current and race off south between your legs.

In a perfect day of dry fly fishing you might hook a dozen or so trees, especially alders. You may hook yourself or your clothing a couple of times too. You may even hook a few trout.

My description above is a gross over-simplification of the challenges and the pleasures to be had from trout fishing. I left out knots and tangles of all sorts. I didn't mention the wind that always blows the wrong way (i.e. in your face). The real insects, especially the biting sorts, are either present in their millions or totally absent. If there are no natural flies on the water, then your feathery imitation is no use at all. Worse still, the flies might be there, the fish might be eating them, but you might not have a suitable imitation in your box. This is every fly-fisherman's nightmare and explains why we carry so many flies and keep buying or tying more.

We encountered this problem too, in a long stretch of dark, slow pools with trees overhanging the far bank but with meadows on our side so that we had plenty of room to cast. The trout were steadily sipping away at flies under the trees. We could reach them, but they ignored our offerings. Some of the most confident fish were making bloops and gulps from the secure cover of roots and branches, right against the bank. Perhaps they get fished for a lot and have learned that they are safe there? A gust of wind revealed the real answer. Thousands of tiny green-fly (aphids) were falling off the sycamore leaves into the river. The trout were only rising under sycamores, not willows or alders. The flies were tiny. We had green flies, but they were not small enough. Even if we had them they would have been too tiny to tie on the line. The knot would have been bigger than the fly! All the same, Alex found the smallest fly he had in his box and just kept casting at the same fish until it gave up. It was the biggest one we caught and certainly the most satisfying.

In our three days, we had the entire range of challenges thrown at us, except drought. We managed to fish for two days, but the third was a wash-out due to floods, so we went over to Wensleydale to see if the Ure was fish-able. It wasn't. We tried a tributary called the River Bain but it was chocolate coloured. We followed it all the way down from Semmerwater to Bainbridge where it joins the Ure and no fish were showing, but we had a lovely walk. And that's the thing really; beautiful scenery, good company and no mobile phone reception. Just perfect.

To see this year's pictures from Swaledale click http://picasaweb.google.co.uk/110446885290724068738/Swaledale2010# .