Spend a week or so in the Tasmanian highlands, and you’re likely to encounter at least one really bad weather day. It’s part of deal really. This prime trout fishery exists because of cold water and lots of it; in turn a function of a climate that can throw snow, rain and gales at you at any time of year.

Our turn came on Saturday. Saturday had stuck out on the forecasts for days; the back end of an Antarctic-spawned low pressure system. With wind speeds averaging 40-50km/h, cold temperatures and near constant rain, it was the sort of day which had even our band of enthusiasts – Mark, Kiel, Justin and I – lingering over a second cup of coffee.

Eventually we headed out, rugged up like something out of a Shackleton expedition, and feeling only a little less adventurous. The hope was to find fish of course, but also some sort of shelter from the weather. After dipping our toes in a couple of small lagoons and investigating possible Great Lake bays, we eventually settled on Arthurs Lake. We’d had a sniff of good fishing there at the start of the same weather system two days earlier, and for all its exposed vastness, Arthurs has numerous shores which are steep and forested – a promise of some shelter from the storm.

A couple of soaking hours of wet fly fishing produced a few browns between the four of us, but by mid-afternoon, we were all damp, cold and seriously considering retreating to the cabin for a hot drink and change of clothes.

Then, on the verge of departing, Mark, impossibly, found some trout rising in the lee of a forested headland. His report was just enough for another half hour of exploration, and that’s all it took to turn the day around. In every semi-sheltered cove, it turned out there were trout rising by the dozen. At first, we weren’t sure if it was rises or rain dripping from trees that was disturbing the water. Then slowly, unbelievably, we realised the reality.

Whatever the trout were rising for was tiny and low floating, and it took several casts and fly changes to get the first take on a size 16 Paradun. Then, as detail resolved, we found we could actually polaroid the trout against the dark backdrop of the forest. The issue was, the trout were so fixated on whatever was on the water, they fed with no real pattern, instead weaving and circling almost at random. Only by landing the fly right in their unpredictable path, would they eat.

Gradually, we all got the hang of it, and the next few hours were as good as Tassie gets. A few fish in, Kiel was retrieving his fly from the mouth of a good brown, when he noticed a mass of insects in its throat. I recognised them as cinnamon jassids – an insect I was only aware of thanks to our columnist Jim Allen’s tips from a few years earlier.

The mystery of a rise in the icy, rain-swept gale was solved. There were jassids by the thousand on the water.

Very little is certain about jassids – when they appear, why, and where. But one of the few things I know is, trout really love them. When the larger and more recognisable red and black jassids are out, the fish eat them in favour of anything else. Even normally appealing items like beetles and duns are all but ignored in favour of these leaf hopper ‘chocolates’. One old timer with decades in the highlands, insists jassids are sweet to taste, so perhaps they truly are Smarties for trout.

And as small as cinnamon jassids are, evidently, they are just as tasty, for it seemed every trout on Arthurs’ shore was eating them. Against all the weather odds, we were enjoying an afternoon of flyfishing that was as good as it gets. While wind blasted the ridgetops overhead, and the rain came through in cold waves, we cast little dry flies to obsessively rising trout for hour after hour. It was sight fishing – and flyfishing – at its finest.

On occasional fishing days, success seems preordained as weather and water conditions line up, to the point lots of trout are all but assured. This day at Arthurs Lake was just about the opposite, and if it proves anything (besides the power of perseverance) it’s the almost miraculous appeal of jassids.