Start by watching, not casting

Chalk streams such as the Test, Itchen or Lambourn are gin-clear, slow and rich in weed. That clarity is a gift and a curse. Trout can see you long before you see them, but you can also see exactly what they are eating. Before you tie on a fly, spend ten minutes on the bank. Kneel low, keep your shadow off the water, and watch the surface. Look for spent mayflies, grannom moths, blue-winged olives or tiny midges. Turn over a few stones and check the underside of weed. A small aquarium net or even a white plastic tray held in the current will reveal nymphs and shrimps. Your first fly choice should come from what you actually see, not from what worked last week.

• Look for insects on the surface, in spider webs, and on bankside vegetation.
• Check the water temperature. Below 8C, trout are more likely to take nymphs.
• Note the light. Bright sun pushes trout into deeper water and under weed.
• Watch for rises before you assemble your rod.

Small dries earn their keep

On a chalk stream, the default dry fly is small. Sizes 16 to 20 cover most hatches, with 22 and 24 for midges and caenis. The trout are not unlike fussy diners: they will ignore a bulky fly if a delicate one is available. Patterns such as a CDC Olive, Parachute Adams, Iron Blue Dun or Pale Watery in sizes 16 to 18 are reliable. If you see olives hatching, try an emerger pattern fished in the surface film. A CDC shuttlecock or a small Klinkhamer can be deadly when trout are taking just below the surface.

Presentation matters more than pattern. Use a 12ft to 15ft leader tapered to 5X or 6X tippet. Cast upstream and slightly across, and let the fly drift back naturally. Avoid drag at all costs. A dry fly that drags will be ignored even if it is the exact colour and size of the natural. If the wind is tricky, fish a shorter line and use the current to straighten your leader. One good drift is worth ten sloppy ones.

Nymphs for the quiet spells

When nothing is rising, chalk stream trout still feed. They are often grubbing among the weed for Gammarus shrimps, caddis larvae and olive nymphs. A Pheasant Tail Nymph, Hare's Ear or a small shrimp pattern in sizes 14 to 18 will take fish. Fish them upstream on a long leader, with just enough weight to get down. A tiny split shot 6in above the fly can help in deeper runs, but keep it subtle.

Sight nymphing is the chalk stream speciality. Spot a trout holding behind a weed bed, then place your nymph a foot or two ahead of it. Watch the trout, not the fly. If the fish moves sideways or opens its mouth, lift. This is far more effective than blind fishing, and it is deeply satisfying. In slow, clear water, a New Zealand style rig with a small dry fly as an indicator can work well, but keep the nymph small and the tippet fine.

Read the rise form

The way a trout rises tells you what it is eating. A gentle sip with a small dimple usually means midges or caenis. Go small: size 20 to 24, and use a fly with a sparse dressing. A head-and-tail rise, where the nose and tail break the surface, suggests an emerger or a nymph just under the film. Try a small CDC emerger or a nymph fished in the surface layer. A slash or splashy rise often means a sedge or a large mayfly. That is the time for a size 12 to 14 Elk Hair Caddis or a Mayfly dun. A boil on the surface, with the trout's back showing, usually means it is taking spinners or spent flies. A rusty spinner pattern fished dead drift will often work.

Match the season, then match the light

Chalk stream hatches follow a rhythm. In April and early May, grannom and olives dominate. Late May and June bring the famous Mayfly hatch, when big duns and spinners get trout looking up. Summer is a time for caenis, midges and blue-winged olives, with evening sedge hatches. Autumn often brings a resurgence of olives and a few large sedges. Light matters as much as season. On bright days, fish early or late, and use finer tippets. On cloudy days, trout are less spooky and will take a slightly larger fly.

• Spring: grannom, olive duns, small nymphs.
• Early summer: Mayfly duns, spinners, emergers.
• High summer: caenis, midges, ants, small dries.
• Autumn: blue-winged olives, sedges, shrimp patterns.

Put it all together and you have a simple approach. Watch first. Match the size and stage of the insect you see. Fish fine and upstream. Change your fly only after you have changed your presentation. Chalk stream trout are not impossible, but they are precise. Give them a small, drag-free fly that looks like the natural, and they will usually reward you.