Mølleåen, also Mølleå, sometimes translated as the Millstream, is a small river in North Zealand, Denmark, which runs 36 kilometres (22 mi) from the west of Bastrup Sø near Lynge to the Øresund between Taarbæk and Skodsborg. The valley contains several country houses and a series of mills which initiated Denmark's industrial development.
The source of the river is Hettings Mose between the lakes of Buresø and Bastrup Sø. Over the next 30 kilometres (19 mi), the river drops 29 metres (95 ft) until it reaches the sea. After Bastrup Sø, the river runs through a swampy area to Farum Sø. Thereafter, for a period it becomes "Fiskebæk Å", passing under the Lyngby Motorway and Frederiksborgsvej before reaching Denmark's deepest lake, Furesø, with a depth of 38 metres (125 ft).
After passing through Frederksdal Storskov, the river runs under Nybrovej until it meets the lake of Lyngby Sø. Between here and the sea, the river falls a further 20 m (66 ft), providing excellent opportunities for water mills. The river winds through the gardens of Sorgenfri Palace to Fuglevad water mill which later became part of the Brede Copper Works. It then proceeds past Øhrholm and Ravneholm to Nymølle which hammered out copper and brass from the mid-17th century. The river then continues to the north past the Frilandsmuseum and on to Brede Museum. It then flows under the Helsingør Motorway to Stampen where there used to be a textile factory, a flour mill and a bakery. After passing through Raadvad, the Millstream finally arrives at Strandmøllen before reaching the Øresund.
As far back as the Viking period, the river was used for milling. From the Middle Ages, the water power of the river was increased by means of dams between the lake of Furesø and the river mouth at the Øresund. In the 17th century, sizeable industrial enterprises were established along the river giving it the reputation of being the cradle of Danish industry. They included mills for the production of textiles, metals, paper and armaments. The factories operated until the 1950s after which they began to close, leaving buildings that were put to other uses. They included the Brede Works, now an industrial museum, and the Strandmøllen paper mill.