The morphology of 3rd‐instar larvae of the genusHydroporusClairville was studied. Generic characters are given to separate this genus from the generaSuphrodytesGozis andCoelambusThomson. Diagnostic characters for the separation of larvae of theHydroporusspecies are briefly discussed and the leg chaetotaxy is analysed so that names are applied to all setae and spines. Descriptions are given of the 3rd‐instar larvae ofH. brevisF. Sahlberg,H. nigellusMannerheim,H, rufifrons(O. F. Müller) andH. striola(Gyllenhal), all based on reared specimens from northern Sweden. A keyfor the identification of Hydroporus larvaeis provided, including also 6 additional species. Data on phenology and habitat of the 4 described species are appended.