The Mararoa river begins in the hills to the west of Glenorchy, and feeds into the Mavora Lakes, before discharging into the Waiau River eight kilometres downstream from 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.
If you get a chance, head down the hill... maybe you have your togs or a fishing rod in the car?