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Geographical location Bernese Oberland
Tributaries Oberaarbach , Treibtenbach , various mountain streams
Drain Aare
Coordinates 668 137  /  157975 coordinates: 46 ° 34 '11 "  N , 8 ° 19' 39"  O ; CH1903:  six hundred sixty-eight thousand one hundred thirty-seven  /  157975
Grimselsee (Canton of Bern)
Altitude above sea level 1908  m above sea level M.
surface 2.72 km²
Maximum depth 100 m


The lake is dammed by two dams

Map Grimselsee.png
Template: Infobox Lake / Maintenance / EVIDENCE AREA Template: Infobox Lake / Maintenance / EVIDENCE MAX DEPTH

The Grimselsee is a reservoir in the headwaters of the Aare in the canton of Bern ( Guttannen municipality ). It is the largest (volume: around 100 million m³) of several neighboring reservoirs from which the hydropower plants of Kraftwerke Oberhasli AG are fed. The lake is just below and on the north side of the Grimsel Pass . The pass road, from which the Grimsel hospice located between the two dams of the lake is accessible, leads a short distance along the lake. The upper end of the lake meets the Unteraar glacier . Shortly before, the Oberaarbach ( Oberaarsee ), which is also dammed further up, flows into the Grimselsee from the left.


The two dams Seeuferegg ( weight wall , 42 meters high) and Spitallamm ( arched weight wall , 114 meters high) were completed in 1932.

Renovation was necessary for the Spitallamm dam because it had had a crack between the air and water sides since the 1960s. Instead of renovation, the construction of a new double-curved arch dam on the valley side next to the Spitallamm wall began in 2019 , initially at the same height as the old wall. After the completion of the new wall, which was planned for 2025 when work began, the old wall will remain in the lake, also for monument protection reasons. However, the new wall is dimensioned in such a way that it allows the new wall to be raised.

KWO plus project

Kraftwerke Oberhasli AG (KWO) is planning, among other things, an enlargement of the Grimselsee with the “KWO plus” project. The dam walls are to be increased by 23 meters and the volume by 75 million m³ (79%). Due to the higher water level of the lake, today's road to the Grimsel Pass would be flooded over a length of 700 m. The project plans to replace the construction of a cable-stayed bridge between two approximately 70 m high pylons over the lake.

Environmentalists were of the opinion that bogs in the upper reaches of the lake , which would be flooded when the Grimselsee expanded, were of national importance and would fall under Article 78 of the Federal Constitution . By decision of December 22, 2015, a chamber of the Bern Administrative Court revoked the concession of the Grand Council from 2012. KWO appealed against the decision. On April 5, 2017, a chamber of the Federal Supreme Court ruled that the Federal Council had not exceeded its discretion when it set the southern border of the Grimsel moorland 27 meters above today's lake level.

Technical data of the dams

Seeuferegg and Spitallamm
Completion: 1932 1932
Lock type:
Seeuferegg gravity dam

Spitallamm arch dam
Crown length: 352 m 258 m
Height: 42 m 114 m
Lock volume: 70,000 m³ 340,000 m³
Catchment area: 74.4 km²
Storage volume: 101 million m³
Surface: 272 ha
Length: 5.3 km
Capacity: 97 m³ / s
Kraftwerke Oberhasli AG, Innertkirchen


In 2005, an article critical of the reservoir expansion argued that pumped storage power plants would help to temporarily store electricity from base load power plants (e.g. nuclear power plants or lignite power plants).

Since then, the electricity market in Europe has changed significantly: the average wholesale electricity price is low; the amount of electricity that is offered at a price of zero cents or even at a negative price has increased sharply. In 2015, 5.2 percent of wind power production in Germany was curtailed (i.e. the rotors were turned into the wind), twice as much as in 2014. Operators of pumped storage power plants can relatively often buy electricity very cheaply and sometimes even for free or at a negative price (i.e. they receive money for purchasing electricity).

Grimselsee Gallery

See also

Web links

Commons : Grimselsee  - collection of images, videos and audio files

Individual evidence

  1. a b Enlargement of the Grimselsee
  2. a b On the Grimsel a second dam will be placed in front of the old one , SRF, August 13, 2019
  3. Homepage
  4. Nature and homeland protection
  5. Bern administrative court revokes the concession to increase the dam wall on the Grimsel
  6. Judgment 1C_79 / 2016
  7. of April 5, 2017
  8. critical article from 2005 on the pumped storage plant (PDF, 1 MB)