Heavy metals in water courses are observed in the selected sampling sites and assessed according to STN 75 7221 Classification of surface water quality (heavy metals - group of indices D). In 1997, heavy metal was assessed in 108 sampling sites. Total assessment of the heavy metal occurrence in the period 1993 - 1997 is visible in the table “Percentage of the water quality classes according to sampling sites on the monitored water courses”.

Content of heavy metals in some sampling sites of main water courses in the Slovak Republic:
                                                                                                                                                                                              Source: SHMÚ

The worst situation of the heavy metals occurrence is in the east part of Slovakia. Concentrations of heavy metals in the Hornád river Basin was classified at 18 sampling sites. Water quality in the group D was ranged into category IV at 6 sampling sites, into category V at 11 sampling sites and category III was classified in 1 case. From observed elements there were identified high concentrations of mercury, zinc and in some cases copper and arsenic. The occurrence of heavy metals is caused by metal processing industry, mining and sewage of Krompachy town.