As early as 1973, the first documented catch of Canadian trout came in Lake Ånnsjön.

The Canadian trout is a so-called invasive species that does not belong in Swedish waters.

Over the years, it has been seen how it negatively affected the natural stocks of trout, but perhaps above all char.

It is unclear how the Canadian trout ended up in Lake Ånnsjön, but for many years, targeted net fishing has been conducted in shallow water during the spawning season in an attempt to - perhaps not eradicate - but at least decimate the population.

Uses high depth nets

Now the County Administrative Board is trying a new method, using high depth nets, to combat the Canadian trout.

- We place the nets, which are significantly higher than normal nets, in the deepest parts of the lake - from 20 to 40 meters deep.

Unlike previous efforts, which were aimed at the shallower places where the Canadian trout spawn in the lake, we are now primarily targeting the large females that are not spawning, says Malte Sjödin from the county board.

How big Canadian trout did you get?

- The largest so far is 17.6 kilos, which could be a record in Sweden.

It indicates that there is plenty of food in the lake.

Only want to catch Canadian trout

To minimize bycatch of the natural stocks in the lake, the nets have extra large meshes.

- I was a little worried that we would get some large char that are found deeper in the lake.

But now we have whitewashed the nets three times and it has been 100 percent Canadian trout, which can be seen as incredibly successful.

We interpret that to mean that the trout and char found at that depth are so small that they can pass through the nets, but of course we miss some of the smaller Canadian char as well, says Malte Sjödin.

One of the 13 Canadian trout that got stuck in the nets when SVT Nyheter Jämtland accompanied them out on Lake Ånnsjön.

Photo: Fredrik Lundmark/SVT

Devastating if the Canadian trout spreads

So far it does not appear that the Canadian trout has spread further from Lake Ånnsjön, which would be devastating if that happened according to Malte Sjödin.

- We do not think it is possible to completely eradicate it from Lake Ånnsjön.

But should the Canadian trout spread further downstream, and spawn in the lakes there, we have a problem that cannot be solved.

Here at Ånnsjön, we have the chance, on the first lake closest to the mountains, to slow down the development before it goes too far.   

In the clip above, you can follow along on Lake Ånnsjön as Malte Sjödin and Tommy Albertsson clean the nets.