Medium-sized to large larvae, up to 9 mm long.
Antenna with 6 segments; segments consecutively smaller; segment 6 vestigial. Blade shorter than flagellum. Lauterborn organs distinct, about as long as segment 3 or slightly shorter.
Labrum with SI coarsely or sometimes finely plumose. Labral lamellae simple, triangular, weakly sclerotized. Pecten epipharyngis consisting of 3 simple, sclerotized, smooth spines. Premandible with 2 apical teeth and more or less pronounced inner accessory tooth; brush absent.
Apical tooth much shorter than combined width of 3 inner teeth. Seta subdentalis apically serrated or indented. Branches of seta interna are smooth.
Mentum with 2 median teeth and 6 pairs of lateral teeth. Ventromental plate well developed; beard absent.
Maxilla with longitudinally curled lacinial chaeta, often forming a nearly complete cylinder. At most one lamella of galea serrated. Pecten galearis well developed.
Body with well developed procercus, sclerotized posteriorly, with 7 apical setae. Anal tubules shorter to slightly longer than posterior parapods.
Larval Hydrobaenus live in the littoral zone of lakes (especially oligotrophic ones), ponds, puddles, ditches and less often in rivers and streams. Most species are typically boreal (northern). The genus is restricted to the Holarctic.