Organotin compounds are entering the aquatic environment due to their use in antifouling paints on boats and from municipal and industrial wastewaters [1]. Tributyltin (TBT) is highly toxic to aquatic life, particularly to marine molluscs (oysters) [2] and gastropods, leading to observed declines of dog-whelk populations on various coasts [3]. Chronic toxic effects on these organisms occur at aqueous concentrations of a few ng/1. TBT, dibutyltin (DBT), and monobutyltin (MBT) have been detected in the aquatic environment. Increased concentrations of TBT in water, sediment, and biota have been linked primarily to pleasure boating activities. In the water column, TBT concentrations were reported to lie in the high ng/1 range for marinas, and in the low to medium ng/1 range for open waters [4, 5]. TBT residues in sediments were found to be considerably higher, typically in the high /~g/kg range [4 6], and total butyltin concentration was shown to decrease with depth in sediment cores [7]. In the water column, TBT is biodegraded by successive dealkylation reactions leading to DBT as the principal degradation product with lesser amounts of MBT [6, 8]. In sediments, degradation was reported to be much slower with half-lives of 4 to 5.5 months [6 8]. To date, little is known about the occurrence and persistence of organotin compounds in sediments. Here, we report on the vertical distribution of a series of butyltins and phenyltins in the sediment of freshwater marinas of Lake Lucerne, Switzerland. The occurrence of phenyltin residues has not been previously reported. By using radiocesium isotopes in the sediment, we derive geochronological data. Con-