Lakes in catchments of rivers can be sinks or sources of ecologically relevant substances. The distribution of oxygen to deep waters and transport of nutrients and other substances from the deep layers, and chemical transformation of substances is controlled by the circulation patters. Some lakes are meromictic, i.e. they do not experience a full overturn in winter. A deep layer of particular chemical conditions can establish (Figure 1). Especially mining lakes tend to show this feature [1]. Vertical transport between layers is strongly restricted. Hence isolated from direct exchange with the atmosphere monimolimnetic waters usually get depleted of oxygen after sufficient time and develop differently to the mixolimnion in terms of geochemistry.