This article contributes to understanding processes occurring in long-time abandoned, shallow and unremediated mining lakes exemplified by the Colorful Lakes near Wieściszowice, Southwest Poland.

Temporal and spatial water chemistry variation and stable isotopic composition has been investigated in two sampling campaigns in wet and dry seasons. Novelties relating to these Lakes are that for the first time, depth and temporal dependent samples were studied chemically and isotopically. Water samples from various depths of the lakes and drainage water were analyzed for main ions, trace and semi-metals as well as sulfur and water isotopes. Data were interpreted statistically and with the chemical-thermodynamic code PHREEQC.

Processes in the lakes are similar, resulting from rain and groundwater infiltrating the rocks and mine residues and leaching efflorescent salts. Differences result from the lakes’ depth, altitude, and source of inflow. They cause the Blue Lake to be in the Al- and the Yellow and Purple Lakes in the Fe-buffer-range. These lakes’ characteristics result either in stratification, evaporation influence or a well-mixed pit lake identified by the isotope variability. Isotope results further identified bacterial sulfate reduction throughout the lake water column during spring and summer. Saturation indices show an undersaturation in relation to most phases, and the species distribution in the lakes mirrors their individual buffer environment.