There is a fortnight or so most autumns on the big reservoirs where the fishing changes completely and the biggest fish in the water become genuinely catchable. It happens when the trout switch onto fry, and if you time it right it is the best chance you will get all year at a really good fish.
What is actually happening
Through summer the coarse fry that hatched in spring have grown into dense shoals, and as the weed dies back in autumn they lose their cover. They pack into the margins, around boat moorings, along dam walls and into any remaining weedbeds.
The trout work out very quickly that a shoal of fry with nowhere to hide is a far better meal than a buzzer. Once they switch, they stop looking at small flies almost entirely and start hunting.
The fish that make this switch most decisively are the big ones. A three or four pound rainbow can take advantage of fry in a way that a stock fish cannot, and the biggest browns in a reservoir are often almost entirely fish eaters by autumn.
How to spot it
You do not need to guess. Fry feeding is visible if you know what you are looking at.
Look for showers of fry breaking the surface, which is fry scattering from something underneath. Look for gulls and terns working a tight area, because they are on the same fry. Look for heavy boils and swirls rather than neat rises, and for the odd stunned or dead fry floating on the surface, which is a very reliable sign that a trout has smashed through a shoal.
The margins near the dam, around aeration towers, along reed edges and in any corner where wind pushes the fry are the places to look first.
Fishing it: match the size, not just the shape
The commonest mistake is fishing too small a fly. Fry patterns should look like the fry that are actually there, which by autumn are often two to three inches long. A little size 10 lure is not it.
Minkies, zonkers, Humungus patterns and big white or olive baitfish imitations all work. What matters is profile and movement more than exact colour. If you can only carry two, take a white one and a natural olive one.
The dead fry trick
This is the one that catches the biggest fish and the one people skip. When trout smash a fry shoal they injure and kill far more than they eat, and those dead fry sit motionless in the surface film. The trout come back later and mop them up at leisure.
So fish a static, buoyant dead fry pattern in the film and leave it completely still. No retrieve at all. It goes against every instinct and it works. A floating fry pattern left sitting among the debris of a fry massacre is how a lot of very big autumn trout get caught.
Lines and retrieves
A floating line covers most fry situations because the action is usually near the surface or in the margins. An intermediate is useful when the fish are working slightly deeper along a dam wall.
Retrieve with pace and irregularity. A fry escaping is not moving steadily, it is bolting and pausing. Long strips with pauses, and be ready for the take on the pause, which is when most of them come.
Do not leave the fish to find fish
If you find a fry feeding area that is producing, stay in it. The temptation to keep moving because the boils have stopped is strong, but fry shoals stay put and the trout come back to them repeatedly through the day. Sit on it.
Timing the season
Fry feeding builds from late August, peaks through September and into October, and tails off as the season closes on most reservoirs. It varies year to year with how the fry have done and how quickly the weed goes.
Ring the fishery and ask. Any decent reservoir will tell you honestly whether the fry feeding has started, and it is worth timing a trip around the answer rather than turning up and hoping.
Sarah Marsh came to fly fishing through her father, who kept a rod on a small syndicate water in Devon. She spent her teens fishing stocked reservoirs and gradually worked her way toward wild fish on moving water – first on rain-fed freestone rivers in Wales, then on the Hampshire chalk streams she now considers home water.
She holds a level 2 APGAI fly casting qualification and guides informally on the River Test and, from June to September, on a private beat on the River Tay for Atlantic salmon. Her personal best brown trout came from the Itchen at 4lb 1oz; she’d sooner not talk about the salmon that came off at the net last August.
At The River Bend, Sarah writes the game fish species guides, fly fishing technique articles, and the legal content covering trout and salmon regulations.
Covers: Brown trout, rainbow trout, sea trout, Atlantic salmon, fly fishing, chalk streams, Scottish rivers, close season and regulation articles