The life cycle and aspects of the biology of Baëtis macani, a species restricted to Fennoscandia, are described from a small lake and its outflow at 1330 m a.s.l. near Finse, Norway (60°36' N, 7°30' E). Additional data are presented from Øvre Heimdalsvatn, a subalpine lake in the Jotunheim mountains (61°26' N, 8°52' E). At Finse the ice free period lasts only 3 1/2 months during which time nymphal development and emergence occur. It is probable that after winter diapause egg hatching occurs at the end of June in connection with the rise in temperature at ice break. Nymphal growth is rapid. Emergence begins in mid-August, reaches a peak during early September and continues until the beginning of October, shortly before ice forms again.