FNDC's general manager infrastructure and asset management Jacqui Robson said the dump was being investigated, with involvement from Northland Regional Council and DOC.
"The volume of rubbish is huge, at least 30cu m and includes several car bodies. The site is very steep and inaccessible, requiring a detailed removal plan to be prepared," she said.
FNDC had received at least three complaints from the public about this particular patch, but Ms Robson said dumping had been ongoing along the road for several years. She could not comment on how the rubbish was being investigated, or how many parties she thought had contributed to it.
"The dumping is under investigation and I don't wish to prejudice the investigation's outcome," she said. "The council wishes to identify all perpetrators and prosecute them to the fullest extent of the law."
FNDC were not the only council struggling with illegal rubbish dumping. In Whangarei, complaints about rubbish being left outside rural dumps have increased almost four-fold after a cut in transfer station hours last year.