Some people sought the advice of Fish and Game, who together with the Te Arawa River Iwi Trust, Tauhara North No2 Trust, Taupō District Council, Mercury Energy and Fonterra all supported the rāhui.
Forrest said recent tests had shown the E. coli levels of the river had returned to normal.
Work was taking place to monitor the river's health.
Last year, five sensors were placed in the river by Waikato River iwi and their partners to monitor from Te Waiheke o Huka (Huka Falls) to Pohaturoa (Atiamuri).
Eugene Berryman-Kamp, chief executive of Te Arawa River Iwi Trust, said the "RiverSense" sensors provided information 24/7 on a range of indicators of river quality including dissolved oxygen, temperature, PH, turbidity and nitrates.
The real-time data was available on a digital dashboard and ultimately would be used for modelling land use change and the effect of that on water quality.
A second monitoring scheme, the Ruahuwai Takiwa project, had now been funded by the Waikato River Authority and that final report was due early 2020.
Roger Pikia, co-chair of the Waikato River Authority and chair of the Ngati Tahu – Ngati Whaoa Runanga Trust and TARIT, said river iwi and their partners were undertaking many environmental projects around the health of the river and its flora and fauna, as well as bringing stories of the river to life for the iwi to share with all New Zealanders.