Usserød Å, the principal drainage of Sjælsø Lake. is a stream in North Zealand to the north of Copenhagen, Denmark. It is approximately 9 kilometres long, drops 18 metres and is joined by Donse Å before itself flowing into Nive Å on its way to the Øresund at Nivå. It passes through the protected Usserød Ådal and the town of Hørsholm. Several watermills and early industrial sites are located along its course, the largest being Usserød Textile Mill.