The Lemmenjoki River (Finnish: Lemmenjoki, Northern Sami: Leammi) is a river in the northern part of the Finnish province of Lapland. Some 80 kilometers long, it flows from Nautajänkä, via Lake Paatari, terminating in Lake Inari.
The name of the river comes from the Sami word "Leammijohka", meaning "warm river". Due to an erroneous folk etymology, the form Lemmenjoki is often associated with the Finnish word lempi (genitive form lemmen), meaning "love".
The Lemmenjoki National Park derives its name from the river.