The river feeds into the
Mavora Lakes and discharges into the
Waiau River eight kilometres downstream from where it leaves
Lake Manapouri. Water from the Mararoa River is fed into the Waiau River by a control structure at the confluence of the two rivers. This is used to control the level of Lake Manapouri for hydroelectric power generation. The river has been identified as an
Important Bird Area by
BirdLife International because it supports breeding colonies of the
endangered black-billed gull.
Didymo, an invasive organism discovered in New Zealand in 2004, has been found in the river. ==See also==