We tested the impacts of most common sample preservation methods used for aquatic sample materials on the stable isotope ratios of carbon and nitrogen in clams, a typical baseline indicator organism for many aquatic food web studies utilising stable isotope analysis (SIA). In addition to common chemical preservatives ethanol and formalin, we also assessed the potential impacts of freezing on delta C-13 and delta N-15 values and compared the preserved samples against freshly dried and analysed samples. All preservation methods, including freezing, had significant impacts on delta C-13 and delta N-15 values and the effects in general were greater on the carbon isotope values (1.3-2.2aEuro degrees difference) than on the nitrogen isotope values (0.9-1.0aEuro degrees difference). However, the impacts produced by the preservation were rather consistent within each method during the whole 1 year experiment allowing these to be accounted for, if clams are intended for use in retrospective stable isotope studies.