Fig. 3a-j: Graphical presentation of essential parameters associated with logistic regression: white vertical line: position of the maximum probability of occurrence (xmax), black bar: optimum range of the given variable, grey-shaded area: range of the given variable that is still tolerated by the species; a) water temperature, b) pH, c) electric conductivity, d) oxygen content in the water, e) nitrate concentration in the water, f) water depth, g) biological oxygen demand within five days, h) content of ammonium nitrogen, i) geographic altitude, j) current velocity.