After the waterfall the river runs across the lake of Gautsträsk. Here, the Ammarnäs trout,
profiting of the richness in nourishment offered by the clear water and sheltered by the depth of the lake
, grows up to record size. It is a lake trout, well distiguishable from the brown trout for the absence of red spots.
After spending the winter in the depth of the lake, it runs into the river during the warmer season.