Water quality in lakes

Since the 1980s, the quality of the water in Swiss lakes has improved. However, several lakes continue to be increasingly over-fertilized and adversely affected by oxygen depletion. Contamination by micropollutants is a new challenge. The FOEN provides status reports and figures for the most important natural lakes on this page.

The development of wastewater treatment and the ban on phosphate in laundry detergents have substantially lowered pollution and nutrient loads in lakes from settlement areas. However, there is increasing pollution from synthetic organic trace compounds that are not readily biodegradable.

The decrease in nutrient loads occurred, for example, with the decline in phosphorus levels in Swiss lakes from the mid-1970s to the 1980s (depending on the lake). However, several lakes in areas with intense livestock farming or extensive areas of cropland still have excessive phosphorus levels.

In many lakes, the oxygen supply in deep water improves as phosphorus concentrations fall. This is a continuous process. Nevertheless, the requirements of the Waters Protection Ordinance have either not yet been met or were met solely through artificial aeration in several lakes. Lower oxygen levels have been observed in the deep water of individual lakes due to reduced mixing.

Information about water quality in individual lakes

The FOEN publishes status reports and figures for the most important natural Swiss lakes. They are based on the surveys of the cantons, international water protection commissions, Eawag and the water supply of the City of Zurich.

Bathing water quality

Die hygienische Wasserqualität der Schweizer Flüsse und Seen ist gut. In den Seen und Flüssen kann fast überall bedenkenlos gebadet werden.

Water quality data for individual lakes

Further information

Last modification 19.04.2020

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