Interesting developments being put into gear by Surfrider. The crux of it boils down to this: the dune at North Narrabeen has been overzealously protected and is now locking up sand that would otherwise flow out to the wave zone. The result is deteriorating wave quality at Northy, it being dependent on the sand flow.

Manly Daily give it the fluff job: https://manly-daily.whereilive.com.au/news/story/give-a-great-wave-a-bre…
Surfrider simply categorise it on their website: https://www.surfrider.org.au/campaigns/endangered-waves/1-north-narrabee…

It's a classic situation of a tampered beach. Massive erosion at one end, too much sand at the other. The only solution seems a perpetual balancing act swinging between antagonism and acquiescence by council and stakeholders.