Transcript
I'm Geoff Owen, secretary of the lake management committee for Trawsfynydd Lake.

Back when the power station was generating the water used to be warm. Since it stopped, the temperature has dropped and the lake has gone back to its natural temperature. The insect life, of course, had to change during this period.

The fishing is more like it used to be now - a natural insect life type fishery. The fish are coming back to feed on the surface and not going back to the depths where the water was colder back when the power station was generating.

So we're seeing a lot more top-of-water fishing now. Competitive anglers have experienced a very strange change, because Trawsfynydd always used to be a deep water fishing environment, but now the tactics they have to apply are totally different.

As for flora and fauna, we're looking to introduce some areas where we may be able to put mayfly, duckfly and dragonfly lava. That all has to be done in accordance with the rules the Environment Agency imposed on us. We're also working closely with the RSPB as we've got some native birds in this area which you don't find in any vast numbers all over the rest of Wales.

There was always a lake here, albeit much smaller. When Maentwrog, the hydro-generating station at the bottom of the valley, wanted water to generate electricity down there, they put a dam at the bottom of the lake, which is how it was created originally.

The nuclear electricity industry decided it would be an ideal place to put a nuclear power station, using the water here as a natural radiator, pumping water into one area and sucking it out of another. The water was only ever used for cooling, not in the reactors. They convert steam into water to pump around and use in the turbines.

In some cases, people believed because the water was warm, the fish used to grow faster, but I don't think that was really the case. We have heard all the jokes about the two-headed fish, but I've worked at the power station for a long time, very closely with those who do the biological sampling. They've been taking milk from cows, collecting mosses and grasses and the fish from the lake - brown, rainbow trout, perch, pike, eels. They collect them, boil them down into almost nothing, grind it up into powder and sample it and there's absolutely nothing in the sample. You'd get more from a cup of coffee in the morning than you would from any of the fish here.

There is an issue regarding the silt at the bottom of the lake and the fish that eat the plankton from the muds, but they've never seen anything in the samples.

Until you've been here, seen and caught the fish, you won't see the quality of the fish, which is fantastic. I've fished here for a long time - on a summer's evening, when the sun's going down I can't think of a better place to be.

Fishing on Llyn Nantlle with On the Fly.