This is a fun roadside run that starts at Maruia Falls and ends 1 km before the confluence with the Buller River. Starting at the falls is exhilarating, but the rapids are generally straightforward. The run only takes a few hours, at just over 10km.
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Logistics
Take out: Make sure to scout the take out! It’s just above a small rapid following a blind turn. The eddy is easy to catch but it’s also easy to blow on by if you aren’t paying attention and possibly end up in the Buller..
Directions to take-out: Drive 1.6 km south of Sullivans Bridge (junction of HWY 6 and HWY 65). Where the highway bends to the southeast there is a small gravel pullout into the grasses with room for several cars. There is a rough track through the bramble on the south side of this pullout. Once through the sharp stuff continue down until you are 5 meters above the river. Turn upstream and walk another 25 meters on a track that drops more easily to the true right of the Maruia River.
Put-in: Right at the bottom of Maruia Falls. Take the short track (2 min) following signs to the ‘best view’ of the falls. There’s a giant eddy with re-circulating deadfall (trees) you can float amongst. But don’t get to close to the falls — there are powerful hydraulics!
Maruia River (II) below the falls
This is a fun class 2 float with some class 2+ moments, mainly when the river drives hard into walls on a turn. There’s also plenty of flat water, easy rapids and a stunning gorge section with deep green pools full of giant boulders.
Be aware of tree strainers on the banks. As of Feb 2019 there are a few that are mid-rapid to watch out for, but all are easily avoidable.
If you have the skills you can skip the take-out and continue 1km to the confluence of the Maruia and the Buller to do the O’Sullivans to Ariki falls run (III). This is the classic Buller Gorge run.
Gauge
Visual. We ran it in early Jan and when it was lower in early Feb. Rain was pretty scarce and the Buller was running low, but this run on the Maruia only had the occasional scrape on the bottom of the boats. Still plenty of water.
Some flat water on this gorgeous stretch of river 
At the put in, float around at the bottom of Maruia Falls 
Floating around the giant eddy filled with logs (and in our case, a dead pig, too…) 
A bit of fun on the way down 
Cooling off in a side stream 
Deep water in the gorge
Higher in the Maruia, is a II/III+ run that is popular with hardshell kayakers. See the information on the Whitewater NZ website for “Maruia – Chrieghton Road to SH65“