The Green Party says league tables of the country's rivers confirm intensive farming is the main source of water pollution.
The Ministry for the Environment has published three tables that list 77 river sites according to water clarity, animal life and the amount of run-off nutrients they carry.
Some of the worst polluted rivers are the Waitara, Whanganui and Manawatu rivers in the lower North Island.
A Green Party spokesperson, Kevin Hague, says it's a great first step to make the information available.
But Mr Hague says the data is two years old and it's likely many of the rivers surveyed are now in even worse shape.