A survey of 2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine (Irgarol 1051) and organotins, used as biocides in antifouling paints, was carried out in German marinas of the North and Baltic Sea. Highest levels of the s-triazine herbicide were found in Baltic Sea marinas where water exchange was restricted (water up to 440 ng/l; sediment about 220 ng/g dry weight), while in the North Sea marinas with higher water exchange rates lower concentrations were encountered (water 11–170 ng/l; sediment 3–25 ng/g dry weight). Although the application of the antifouling agent tributyltin (TBT) was banned for small vessels (<25 m) in Germany and other countries in 1989, significant levels of TBT between 570 to 17 000 ng/g dry weight, lower concentrations of triphenyltin (TPT) of up to 3800 ng/g as well as the TBT degradation products dibutyltin and monobutyltin occurred in sediment samples of the Baltic Sea marinas. In the North Sea marinas with stronger water exchange the TBT sediment levels ranged from about 80 to 720 ng/g dry weight. This study shows parallel contamination patterns of Irgarol and organotins in North and Baltic Sea marinas and the persistence of several organotins in these sediments about eight years after the ban. A seasonal dependence of Irgarol 1051 concentrations was found both in the water and sediment samples, with maxima during the periods March–May/July–September, while during the winter period December–January low values were encountered though measurable amounts remained in the sediment. A mean value of the partitioning coefficient log KOC=3.3±0.72 was inferred from the water and sediment concentrations determined in seven Baltic Sea marinas.