Alnsjøen, reservoir
Alnsjøen is a small lake in the wooded area called Lillomarka in Oslo, sitting about 238 meters (780 feet) above sea level. The water covers roughly 0.41 square kilometers and reaches about 32 meters (105 feet) deep, surrounded by dense forest on all sides.
The lake once served as a drinking water source for Oslo, with water carefully managed to keep it clean and safe. In 1930, a channel about 700 meters long was built from the nearby Breisjøen lake by blasting through rock to supply this one.
The name Alnsjøen comes from the word 'aln,' meaning bend or meander, reflecting the water's natural form. Today, the lake serves as a quiet place where locals walk, observe birds, and enjoy time in the forest.
The lake is accessible on foot and mainly used for hiking and nature watching, so bring sturdy shoes since the paths around it are natural and sometimes uneven. The best time to visit is during the drier months of summer and fall, when the trails are easier to navigate.
This is one of only a few places in Norway where flytegro, a rare floating bog, naturally occurs in and around the lake. This unusual feature creates distinct ecological conditions that attract geologists and nature enthusiasts.
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