Massive growth of sub-ice algal assemblages was recorded at two stations under first-year ice off northeast Greenland using a Remotely Operated Vehicle equipped with cameras. The assemblages mainly consisted of the diatom Melosira arctica (Ehr.) Dickie. A station sampled at the beginning of June 1993 revealed two forms of growth, curtain-like and rope-like, but with many intermediate types along the entire 150 m transect. The algal distribution was patchy. No significant sympagic fauna was found close to the algal masses. At a station sampled in the middle of July, similar algal concentrations seemed to be disturbed by ice-melting processes. Two casts under multi-year ice flows failed to show any algal aggregations. The observation of algal assemblages under first-year ice is in contrast to earlier reports from the Barents Sea where they have been recorded exclusively under multi-year ice. © 1995 Springer-Verlag.