Figure 18 in Diversity, distribution and community composition of fish in perialpine lakes – "Projet Lac" synthesis report

Figure 18: Zone of low oxygen in Lower Lake Zurich has been increasing in severity and vertical extent since around 1990, offsetting gains of oxygenated deepwater habitat that would otherwise be associated with the reduction of eutrophication. Severe hypoxia also occurred between 1940 and 1960 and is believed to be caused by a combination of elevated nutrients and inverse stratification in winter during this period [50]. Isobars for dissolved oxygen concentrations of 1 and 4 mg/L are indicated. Data source: Canton Zurich, Amt für Abfall, Wasser, Energie und Luft (AWEL) and Wasserversorgung Zurich. Black bars on the right side: depth distribution of Projet Lac fish catches by abundance (net per unit effort catch).