Years after the original resource consent ran out, a new hearing is under way for permission to continue discharging stormwater from Whanganui Prison to a water channel.
The water channel links lakes Pauri and Wiritoa at Kaitoke.
The original discharge consent ran out in December 2013, but the Department of Corrections applied for fresh consent within six months so discharge has continued legally since then.
The hearing for the new consent from Horizons Regional Council began on Tuesday before a panel of three independent commissioners, led by chairman David McMahon.
McMahon said he was "very fortunate" to be joined by fellow commissioners Liz Burge and Sharon McGarry.
"They have a wealth of experience, not only in hearings, but in two topics that are probably going to be to the forefront of decision making for this hearing, those being iwi and cultural matters, and water quality and ecology matters," McMahon said.
"That makes my job a lot easier, and it allows me to steer the ship, so to speak."
The Department of Corrections is seeking consent until 2044, with the application being prepared by consultants Boffa Miskell.
At present, both Pauri and Wiritoa lakes are subject to algal blooms, but, according to the application, the prison discharge is "a relatively small contributor" to their overall water quality.
Stormwater management specialist Peter Cochrane, who will present evidence on behalf of the applicant, said the adverse effects of the discharge on water quality in Lake Wiritoa will be "negligible", and will improve water quality to help meet the One Plan Regional Plan targets for deep coastal lakes.
Submissions from the Department of Corrections and its expert witnesses are expected to last until around lunchtime on Wednesday. From there it will be the turn of submitters, led by Ngāti Apa and Te Rūnanga o Tūpoho, to speak on their submissions and evidence, and answer questions from the commissioners.
This will be followed by supplementary evidence from expert witnesses Horizons' freshwater manager Logan Brown and senior consents planner Natasha Adsett on Wednesday afternoon, with the hearing set to close on Thursday morning.
McMahon said the commissioners had "a very useful first visit" to Whanganui Prison on Monday.
"We had a visit inside the wire, which was quite intimidating I must say," McMahon said.
"I've definitely decided to put any criminal activity on hold for the time being.
"We then went outside the wire and had a look at a number of facilities, including the discharge outlet which goes into the channel, and we went around both lakes before ending up at the camp ground."