The seasonal variation of cadmium, copper, lead, zinc and ash content in above and below-ground parts of eelgrass (Zostera marina L.) was studied at three locations in the Limfjord, Denmark.Heavy metal concentrations in eelgrass from the three locations differed significantly, and reflected either the concentrations in the sediment (Cu, Pb, Zn) or the concentrations in the ambient water (Cd).Above-ground parts of eelgrass contained significantly higher concentrations of cadmium, copper and zinc than beloww-ground parts, while no significant difference was observed for lead.Ash content in above-ground parts of eelgrass showed a significant seasonal variation with lowest ash content in spring. A general seasonal variation pattern of heavy metal concentrations in above and below-ground parts of eelgrass was observed. Maximum concentrations were encountered in late winter—early spring and minium concentrations in the autumn. This seasonal variation pattern on heavy metals can be explained by the growth dynamics of eelgrass.