The distribution pattern of ecotoxic trace metals Cd, Co, Cu, Hg, Ni, Pb and Zn in marine lakes (Malo jezero and Veliko jezero), which could be harmful for the water ecosystem biodiversity of the Mljet National Park, will be established. By measuring trace metal concentrations in water column of the marine lakes (Cd, Co, Cu, Ni, Pb and Zn - voltammetry; Hg - atomic absorption spectrometry) the scale of anthropogenic influence should be obtained. Water mass circulation and currents influence trace metals distribution. Therefore, device for current measurement will be deployed in order to get insight of water movement. It will be combined with numerical models to forecast the transport of pollutants from natural and anthropogenic sources. Data loggers for temperature and salinity measurements will be deployed in the deepest part of Malo jezero where probably subaquatic spring is present, to record possible fresh or marine water incursion.