Aurajoki ([ˈɑu̯rɑˌjoki]; Swedish Aura å) is a river in south-western Finland. It originates in Oripää, and flows through Pöytyä, Aura, Lieto, and ultimately the city of Turku before discharging into the Archipelago Sea. The total length of the river is about 70 kilometres (43 mi), and it contains eleven rapids, the biggest of which is Nautelankoski at Lieto. The reserve tap water for Turku Region is drawn from Aurajoki, the city's secondary waterworks being situated by the Halinen rapids.
The waters of the Aurajoki are brown. Situated in an agricultural zone, the river is made turbid by surface runoff from nearby farms with eutrophication as the biggest threat. Its condition has been improving since the 1970s and Aurajoki is now clean enough to support salmon.