An action plan has been approved to improve the water quality of Lake Tikitapu, near Rotorua.
It is still safe to swim in what's known as the Blue Lake but there are indications its water quality has been worsening since monitoring began in 1992.
The Rotorua Te Arawa Lakes Strategy Group has approved the action plan.
One of the group's members, Warwick Murray from the Bay of Plenty Regional Council, says most of the key actions have already been taken to reduce nutrient levels in the lake, including sewerage reticulation.
He says the situation will be monitored during the next year.