Alixzae Lewis, 9. swims at Horseshoe Bend in Tokomaru. Research has found Manawatū's rivers are getting cleaner.

Manawatū's rivers are officially getting cleaner, with a study finding measures such as fencing and riparian planting are likely making a big difference.

There is also evidence showing improvements at pollution points, such as wastewater discharges, is cleaning up rivers.

An independent report commissioned by the Ministry for the Environment and Horizons Regional Council, and released in February, showed there had been an improvement in the swimmability of Manawatū and Whanganui rivers in the decade leading up to 2016.

The report, put together by LWP Ltd and reviewed by both NIWA and Statistics New Zealand, used data collected from 231 river sites throughout the area.

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The study found there had been a reduction in sediment and E coli in the region's rivers. Lakes were not measured.

The report stated the evidence linking on-land measures, such as planting trees and fencing waterways, and improving waterways was weak, mainly because it was hard to measure. However, it was still considered safe to say those measures had a positive impact.

"The study therefore provides weak but positive evidence that [Horizons'] interventions have contributed to the observed improvements, and suggests that a package of mitigation measures implemented at many locations across a region can produce regional-scale water quality improvements."

The strongest evidence was taken from places near identifiable pollution points, such as where wastewater goes into rivers, the report said.

Ministry for the Environment deputy secretary of water Cheryl Barnes said the study showed lots could be done in a short time.

"The key was taking a planned, whole-of-catchment approach and prioritising effort and investment where it would make the most difference.

"This information will be a useful contribution to national freshwater policy development."

Horizons Regional Council natural resources and partnership group manager Dr Jon Roygard said the report showed the benefits of long-term thinking, such as the council's Sustainable Land Use Initiative.

The scheme came into effect following the big storm of 2004, works with farmers to reduce erosion on farms.

Farmers get individual plans, and are given incentives paid for through both rates and central Government funding, to reduce erosion.

Roygard said 683 different plans, covering more than 500,000 hectares of land, had been developed. That had resulted in 14 million trees being planted, and more than 570,000 metres of waterways being fenced, he said.

"Further fencing and planting has also been completed through freshwater grants and a clean-up fund project through the Manawatū River Leaders' Forum."

The research showed how targeting highly erodible land, such as through the land use scheme, could make a big difference, he said.

The report came just as Horizons launched its "Spruce up your Swim Spot" competition, where people can vote for their favourite swimming location in the wider Manawatū-Whanganui area to get some tender loving care.

Horizons chairman Bruce Gordon said Mosquito Point in Whanganui won last year, and has since got a new changing shed and seating, steps to help swimmers access the river, and some vegetation cleared.

The eight swim spots people can vote for are Ōhau River at Gladstone Reserve, Horseshoe Bend, Pohangina River at Raumai Reserve, Manawatū River at Hopelands, Rangitīkei River at either Mangaweka or Vinegar Hill, Lake Wiritoa, or Whanganui River at Cherry Grove.

People can vote via a poll on Horizons Regional Council's Facebook page, with the poll closing on March 25.