The Ainzera river (Mirselec Ainzera ainos) is a river in Masalne.
The Ainzera is one of the east-flowing rivers of Masalne, and its course lies wholly within Osagona Province. The river rises in the Mathormagos, the central mountain range of Masalne, and wends its way through several steep valleys before it reaches the coastal plain of the Lavgor Inland Sea, where it then meanders before finally reaching the sea. The total length of the river is 227 km.
Due to the course of the river comprising mainly mountainous regions, the Ainzera is known mostly as a fast flowing stream and some of its valleys have spectacular scenery, where the river has cut steep gorges nearly 60 metres deep, flanked by caves and holes caused by wind erosion. Along its course there are several towns, mostly on the lower course along the coastal plain.