A serious undertaking that has not been completed at the time of writing due to the committing big drops in a remote, box canyon. 
The first reported attempt was in 2018 but after multiple portages around grade V rapids, the first descent team undertook a massive, arduous walk out through private property with their tail between their legs. The 1km section from Deer Park Road upstream of the Waterfall Way includes fast flowing grade II rapids through narrow, tree-lined channels in farmland. The initial 3.5km below Waterfall Way consists of some nice grade III+ rapids with some technical tree paddling and a barbed wire fence but then the creek changes character at a massive, unrunnable waterfall followed by a steepening canyon. The team did a huge portage around the waterfall via farmland on river-right that led back to the river about 1km below the falls. A better option may be to abseil the falls. The section below the falls consists of multiple 4-8m drops in a tight canyon that are committing and difficult to scout or portage. A drone may be helpful for scouting in future descents. 
Deer Park creek enters the Nymboida just above ‘The Silent Pool’ described in the ‘Nymboida- Waterfall Way to Harness Cask Road’ section of this book.
Popularity:★
Quality:★★★
Reliability:★★
Grade:IV+ with a section of possible grade V below the main falls.
Length9km to the junction with the Nymbo plus another 9km down to Harness Cask.
Elevation and average gradient1,100m at put-in, 690m at take-out, 785m at junction with Nymbo 45m/km average for entire trip but the steepest 2km section of the trip drops 87m/km (one of the steepest sections in this book).
Paddling time:Unknown but it would be advisable to carry overnight gear due to the slow progress in the canyon section.
Gauge and level:Visual from the Waterfall Way. Due to the tight nature of the canyon, it is recommended to run this section where there is just enough water to run the rapids below the road. As a rough guide, the Nymboida@Nymboida electronic gauge would need to be at least 4m.
Put-in:Waterfall Way approximately 23km west of Dorrigo.
Take-out:Harness Cask, where Harness Cask Road crosses the river, approximately 6km west of Tryingham Road.
Shuttle:Easy. 45 mins each way. By heading to Dorrigo and then Tyringham Road and Harness Cask Road.
Maps:Map 2 Nymboida River- Waterfall way to Tyringham
Dorrigo 1:25,000