Opportunities for Trout fishing exist throughout Norway. Country wide catch statistics are not available, but the fishing is said to get better the farther west and north one travels.
Trout fishing is often pursued in the mountains, up above the rivers where Salmon and Sea Trout reach. Mountain rivers and lakes are in many cases underfished waters. Consider that there are said to be over four hundred thousand lakes in Norway, a country with a population of under five million people.
The biggest lake is lake Mjøsa, an hour north of Oslo's Gardermoen airport. Mjøsa is one of the deepest lakes in Europe, and the water where Norway's record largest Trout (15.3 kg) was caught.
While many of these waters are accessible by car, a great many can only be reached by hiking for an hour or more. Hiking in Norway and trout fishing in Norway are activities to consider hand in hand.
Hiking in Norway's National Parks can be readily combined with trout fishing as fishing licenses are often available in the national park areas. In Reinheimen National Park, for example, there is both river and lake fishing for trout, with licenses available at the Den Norkse Turistforening lodge at Reindalseter.
It's a fair bet that wherever you are in Norway, the locals can point you to nearby Trout waters. The book Angling in Norway has extensive descriptions of Trout fishing opportunities in Norwegian rivers, if you can find a copy.
Norwegian fishing licenses are needed to fish for trout in Norway. Local tourist information centers often can sell you licenses or tell you where to buy them. Inatur sells licenses for many trout waters in Norway online, though the relevant pages all are in Norwegian.
Methods for fishing trout in Norway range from fly fishing to spinning to worm fishing. All can be quite productive in Norway. When you buy a license, be sure to find out what methods are allowed in the waters covered by the license.