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Return of the salmon to the rivers of   Oslo

Most   rivers and streams in the city of Oslo have had a long history of poor water   quality until the early 1980s. This was reflected in low benthic diversity   and the absence of fish. At the end of the 1970s, considerable efforts were   made to limit industrial discharges, pollution episodes, and urban runoff,   resulting in a substantial improvement in water quality. This improvement in   water quality resulted in major changes to the benthic fauna and fish   populations of the rivers, especially the River Akerselva, which runs through   the city centre. The Atlantic salmon, which became extinct in Oslo in the   mid-1800s, returned to the Akerselva in 1983. Atlantic salmon and sea trout   now spawn in the lower reaches of the River Akerselva, and the river supports   juvenile populations of these salmonids (Saltveit, 2013). 

Jumping salmon in the River   Akerselva, city of Oslo (Photo: @Dan P. Neegaard)