An extensive study on the presence of nine organotin compounds (OTs) in a freshwater foodweb was made, using newly developed analytical procedures in order to obtain insight in accumulation and degradation processes. Tributyltin (TBT), Triphenyltin (TPT) and their degradation products were detected. Zebra mussels, eel, roach, bream, pike, perch, and pike perch and cormorant showed high OT body concentrations. At the lower trophic levels, phenyltin concentrations were higher in benthic species while butyltin concentrations were higher in pelagic species. This indicates that TBT is passed on primarily via the water, while TPT is passed on to a larger extent via the sediment. At the higher trophic levels, net bioaccumulation of TPT was greater than that of TBT, resulting in relatively higher TPT concentrations. High concentrations of biodegradation products of TBT, but not of TPT, were found in the livers of fish and birds, which indicates that TBT is more easily metabolized than TPT. A comparison with literature data of fish lethal body concentrations revealed that fish in the field may be endangered. With birds, the highest concentrations of OTs were present in liver and kidney and not in subcutaneous fat, which confirms that OTs accumulate via different mechanisms than traditional lipophilic compounds. As a whole the OT concentrations found in the foodweb may be considered to be quite alarming.