Average chlorophyll a concentrations in lakes with different trophic status (a) and average chl a in water layers (b). Percentage share of cyanobacteria in lakes with different trophic statuses (c) and in water layers (d). The different italics letters (a, b, c) above the box plots indicates significantly different values at p < 0.05, while the same letters indicate no significant differences. The lower and upper limits of the boxes are the first and third quartiles. The red crosses represent the means and the central horizontal bars are the medians. Points above or below are outliers and the whiskers represent minimum and maximum values.