Continuing north on the Southern Scenic Route from Manapouri, you follow the Waiau River towards Te Anau. On your left is a mix of scrub and farmland, with the edge of Fiordland National Park beyond. There is a cycle/walking track that runs through this area (the Lake2Lake Trail) and you can also access the River by car in three locations. The first of these is Boulder Reach.
Turn off at the signpost from the Southern Scenic Highway and follow the narrow metal road to the River. For views of a section of the River called the Balloon Loop (it looks like a balloon from above), stop near the edge of the cliff. This section of the River apparently featured in LOTR, although there is nothing to signify this outside of an icon on Google Maps. From there you can walk along the shared track northeast to the next road access at Rainbow Reach.