Why small flies win on tailwaters

Ask an angler why they are not catching on a tailwater and the honest answer is usually the same: the fly is too big. Not wrong in colour, not wrong in pattern. Too big.

Cold water grows small insects

A tailwater releases water from deep in a reservoir, so it runs cold and stable all year. That suits midges, small mayflies and scuds, and it does not suit the big stoneflies that freestone rivers produce. The average mouthful in that system is small, and trout tune themselves to it. A size 14 nymph in a river where nearly everything drifting is a size 20 is not a bold choice, it is a conspicuous one.

Clear water removes your margin

Stable flows mean clarity, and clarity means the fish gets a long, unhurried look. In coloured freestone water a trout makes a decision in a fraction of a second. In clear tailwater it can track your fly for a metre before deciding. Everything you got away with elsewhere gets inspected here.

What to change, in order

• Size first. Drop two sizes before you change pattern. It fixes more refusals than anything else.
• Tippet second. Going from 4X to 6X changes how a small fly drifts far more than it changes what the fish can see.
• Weight third. Most missed fish are not eating because the fly never reached them. Add weight before you add novelty.
• Pattern last. If a slim, well-drifted size 20 gets refused, then change the pattern.

Profile beats colour

At size 20 a trout is not reading the shade of your dubbing. It is reading a silhouette against the light: slim or bulky, segmented or smooth, drifting naturally or dragging. This is why we care so much about tying small flies cleanly. A thick size 20 is really a size 18 that has stopped looking like anything.

It is uncomfortable to tie on a fly you can barely see. Do it anyway. The fish can see it perfectly well.