The quality of water in Lake Rotorua is the best it has been since tests began in the early 1990s.
Natural resource operations manager for the regional council, Warwick Murray, said results had been achieved mainly through interventions in the lake and favourable climate conditions.
"These results are great to see, but the way land is used in the catchment needs to change if we're going to achieve long-term sustainable water quality gains," he said.
Water quality is affected by nutrients entering the lakes from a range of natural sources and human activities. Currently 70 per cent of nitrogen entering the lake comes from agriculture.
"We need to stop the nutrients entering the lake. We need to turn off the nutrient tap up in the catchment," he said.
He said to achieve this farmers and landowners in the catchment needed to be involved.
A new advisory group was being set up to help develop new rules and a land-use incentive scheme for the Lake Rotorua catchment area.
The Rotorua Lakes Protection and Restoration Programme - a partnership between the Bay of Plenty Regional Council, Rotorua District Council and Te Arawa Lakes Trust - has been at the forefront of enhancing lake water quality in the region.
The latest recreational water quality report from the Ministry for the Environment shows many of New Zealand's favourite monitored freshwater swimming spots are a health risk and should be avoided.
Bay of Plenty Regional Council water science manager Rob Donald said the lower water quality reflected land use.
"Anywhere there's farm activity near a bathing site you can generally expect a higher risk, whereas if you look at the open coastal sites in the Bay of Plenty, they are of very good quality."
In the study, 24 per cent of freshwater and 13 per cent of coastal beaches in the Bay of Plenty were graded as poor.
Hamurana, the Ngongotaha Stream at Railway Bridge, the Puarenga Stream at Whakarewarewa, the Utuhina Stream at Lake Road and the Waiteti Stream at Ngongotaha all received the poor grade.
To make a change, Mr Murray said farmers must be involved in the process. Rules would be put in place to limit nutrient loads and to ensure the limit was met. An incentive scheme would also be designed to help reduce the impact of the rules and enable farmers to make necessary changes to their operations.
The new group includes 12 to 15 members from the Lake Rotorua Primary Producers Collective, Lakes Water Quality Society, Bay of Plenty Regional Council, Rotorua District Council, Te Arawa Lakes Trust, Office of the Maori Trustee, the forestry sector, iwi landowners and small block owners.
"The group will provide oversight, advice and recommendations on both the rules and incentives," Mr Murray said.
The group will meet regularly to share views, knowledge and expertise.
"Getting sustainable improvements in water quality in Lake Rotorua will take time. It took 50 years to create the problem and it'll take time to fix it. Between our incentive fund and the rules we can reach the water quality targets set by the community for Lake Rotorua."