Taranaki's water is increasingly degraded as it crosses intensive dairying land, monitoring and research has found.
Waterways near the coast have poorer stream health and do not meet guidelines for nitrogen load.
Sewage and other outfalls have been cleaned up in recent decades and Taranaki's regional council says river water quality now has the biggest human impact on coastal waters.
Despite the region's dairy herd growing by about 50% in the past 30 years, the council report found stream life has been maintained or improved since monitoring began 12 years ago.
Council chief executive Basil Chamberlain said while the lower reaches of rivers can never be pristine, he hoped the region's waterways can be brought up to the point where they meet swimming, recreation and other standards most of the time.
He says the region is about half-way through the task of having farmers fence off all waterways.