The Mowhanau, Kai Iwi and Ototoka streams were each given permanent warning signs last December, because their E. coli levels met bathing standards 13, 8 and 4 per cent of the time, respectively.
Horizons freshwater and partnerships manager Logan Brown said the Mowhanau Stream has been monitored and been subject to non-regulatory attempts to improve its water quality for years.
Whanganui District Council was fined for a leak of human effluent into the stream in 2017, but most of the E. coli is usually from sheep and cattle.
The stream will improve over time, but there will be more improvement if more landowners undertake initiatives such as stream planting.
"We welcome inquiries from landowners in the catchment who would like to add to the good work. There is funding available for work in these catchments over the next year," Brown said.
Anyone interested can ring Horizons' freshwater team on 0508 800 800.