[en] Mediterranean Mussel Watch (MMW) is a project for radioactivity monitoring of Mediterranean coastal waters using mussels (Mytilus galloprovincialis) as a bioindicator. Mussels are sessile marine organisms able to filter up to 80 L of sea water daily. Possibility of absorption and accumulation of dissolved/particulate matter from sea water makes them a good bioindicator for environmental pollution studies. Laboratory for Radioecelogy systematically monitores Adriatic coastal waters as a part of MMW project, which includes determination of 7Be, 40K, 232Th, 226Ra,238U and 137Cs, as well as highly radiotoxic naturally occuring radionuclides 210Po and 210Pb. The mussels were collected in spring and autumn periods of 2010 and 2011 at 13 stations including areas under significant fresh water discharges (Rasa, Zrnovnica, Neretva and Ombla Rivers) or areas under potential antropogenic influence (Kastela Bay). After sample preparation 7Be, 40K, 232Th, 226Ra, 238U and 137Cs were determined gamma-spectrometrically, while 210Po and 210Pb were separated on Sr resin. 210Po was determined on an alpha spectrometer after self-deposition on Ag disc, while 210Pb was determined via 210Bi on a gas proportional counter after PbSO₄ precipitation. 7Be, 210Po and 210Pb activity concentrations were higher in spring than in autumn periods for all locations, with the highest activities in the areas under heavy fresh water discharges. Activity concentrations of 40K were practically the same at all locations with no seasonal changes, while 137Cs activities varied significantly. Activities of 232Th, 238U and 226Ra were mostly below the detection limit of gamma-spectrometric measurements.(author)