English-born, Mr Watson (68) had had a 39-year career in fish and game management, of which 37 had been in Otago.
At first, Mr Watson had been manager of the Otago Acclimatisation Society, and from 1990, after government conservation law reforms, was chief executive of Otago Fish and Game Council.
In a statement, the council said Mr Watson had advised that he would retire in the first half of the new year, and the position was being advertised over the holidays, with a January 14, 2018, closing date.
The council aimed to complete the change by the end of April.
Mr Watson knew that Otago's rivers, lakes and wetlands were ``better off for Fish and Game's efforts over the years'', in the face of increasingly intense land use, particularly over the past 15 years.
``I'm certainly not confident that we are on top of water management.''
New Zealand was ``leaving behind a legacy of degraded waterways'' and much stronger leadership from government was needed to deliver the swimmable lakes and rivers most New Zealanders wanted.
It was also ``worrying'' that blooms of toxic algae, including Phormidium, were becoming more common in Otago.
The Otago Regional Council had developed an innovative, good quality water plan, and much related work had already been done, including to develop minimum flow regimes for rivers, but a ``very major workload'' remained to be completed before the 2021 statutory deadline for the ending of deemed water permits from the 19th century.
Working for Fish and Game had been ``immensely satisfying in many ways, always challenging and more than a little frustrating at times''.
It had been satisfying because of the commitment of Fish and Game councillors, staff and our allies to ``do better for freshwater resources'' in Otago and because of support from anglers and hunters, he said.
Otago Fish and Game chairman Monty Wright said Mr Watson would be ``a hard act to follow''.
