SUMMARY1 A dense population of a large (over 6.5mm long), semiaquatic, predatory nematodeAnatonchus dolichuruswas found in the delta of the River Dokka, Norway. This is the first time it has been reported in surface fresh waters.2 Nematode distribution was related to water depth, with maximum abundance (over 24000 ind.m−2) occurring in shallow areas (0.5–2.0m). Sediments at all stations with a high density ofA. dolichuruswere dry and exposed to air and ice during winter and early spring, and overgrown with macrophytes during summer.3 This predator contributed a greater fraction of total numbers and biomass of the nematode fauna than predatory forms in other known freshwater nematode assemblages. It constituted up to 15.6% of numbers and up to 90% of total nematode biomass.4 Anatonchus dolichuruspreyed on Nematoda, small Oligochaeta (mainly Enchyrraeidae) and Chironomidae. It was able to reduce the density of these meiofaunal taxa when present in large numbers in experim