North‐west Kroktjern (Hook Lake). The black cave by the water's edge in the middle of the image, is a man‐made tunnel. It is 164 yards long. It is called Kroktjerntunnelen (The Hook Lake Tunnel). A brook runs out from the other end. This tunnel was made in 1947 to increase the water feed to Lutvann (Lut Lake). Lutvann was drinking water for Oslo from 1918 to 1977, among other drinking water resources. It is no knowledge about the name Lutvann. Lutvann has from a long time ago been understood as very clean water. Today Lutvann is reserve drinking water supply. Thursday, August 13, 2015.

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