Phosphorus concentration in Swiss lakes (in micrograms per litre)
20
40
60
80
100
120
140
160
180
200
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
Lake Geneva
Lake Zurich
Lake Zug
Lake Constance
Lake Geneva
Lake Zurich
Lake Zug
Lake Constance