Rob Forlong, the first chief executive of the three year-old Environmental Protection Authority, has resigned at a time when the government is under pressure from industry to make it easier to develop economic resources after the failure of two seabed mining proposals.

Forlong's departure was announced late this afternoon. He is to take up a role as CEO of the Whangarei District Council.

EPA chair Kerry Prendergast said Forlong seabehad made "a significant contribution to the EPA, and the board and staff are very grateful for his leadership."

He had led the fledgling agency, established in 2011, during the "crucial set-up period", Prendergast said. She was "very sad to see Mr Forlong go."

Forlong led the Environmental Risk Management Authority (ERMA) for six years before being appointed head of the EPA, which has taken on regulation of genetically modified organisms, toxic substances and chemical handling.

The resulting agency became responsible for administering the new Exclusive Economic Zone legislation, creating for the first time a framework to allow the economic exploitation of mineral and other resources in New Zealand's vast EEZ, at 4 million square kilometres, the world's fourth largest marine zone.

Two would-be seabed miners, TransTasman Resources and Chatham Rock Phosphate, spent collectively some $110 million on scientific research and feasibility studies, to have the first seabed mining applications declined owing largely to uncertainty over the marine environment, which was exposed largely by the applicants' own research suggesting mining impacts could be mitigated.

TTR was proposing to mine ironsands in the Taranaki Bight off Patea and CRP wanted to hoover phosphate nodules from the Chatham Rise, some 400 kilometres east of Christchurch.

TTR was so unhappy with the first board of inquiry appointed by the EPA that it has dropped an appeal and will reapply, adding to its $70 million spend over six years to prove it could create a new, low-cost mining alternative source of iron ore for Chinese and Indian steel mills at a time when the global iron ore price is plummeting.

CRP is recapitalising and considering an appeal.