I found what lutefisk is and how it is made:
Lutefisk is made from air-dried whitefish (normally cod, but ling is also used), prepared with lye, in a sequence of particular treatments. The first treatment is to soak the stockfish in cold water for five to six days (changed daily). The saturated stockfish is then soaked in an unchanged solution of cold water and lye for an additional two days. The fish will swell during this soaking, regaining a size even bigger than the original (undried) fish, while the protein content decreases by more than 50 percent, causing its famous jelly-like consistency. When this treatment is finished, the fish (saturated with lye) has a pH value of 11–12, and is therefore caustic. To make the fish edible, a final treatment of yet another four to six days of soaking in cold water (also changed daily) is needed. Eventually, the lutefisk is ready to be cooked.
