Water testing at more than 80 sites across the region has begun, with Horizons Regional Council looking for any potential health hazards.
The annual regime monitors swimming spots in the Manawatu, Rangitikei, Whanganui and Ruapehu catchment.
HRC chairman Bruce Gordon said there was a lot of misinformation telling the public local waterways weren't swimmable.
"This is contradictory to our science, and perhaps more importantly, to the thousands of our community members who enjoy our beaches, lakes and rivers every summer.
However, we recognise the importance of recreational water users being well informed about the potential health risks at these sites, and that is why we have this programme."
HRC implements a traffic light system, used by the Ministry of Health, to test the weekly samples in a lab.
The results, available within 48 hours, are then updated on Horizons' Safe Swim Spots webpage.
If the sample is next to a green location marker, this means the water should be safe to swim in. If the location marker is red, information will be provided to the public as this would be deemed unsuitable for recreational use.
HRC science and innovation manager Abby Matthews said for lakes and rivers to be swimmable, they must have a sample reading of less than 260 E. coli per 100ml.
"Gravel-bed river sites and lakes are also tested for cyanobacteria which is an algae that can be toxic. Horizons will be keeping an eye on this during summer and also reporting these results on the website.
"We do urge public and their animals to stay out of the water if they are at a river and see black mat-like slimy growth on the stones that may also be musty smelling."
Results from the programme are also used to inform policy and work on local waterways.
"For example, water quality trends across the region for January 2007 to December 2016 show an improvement in E. coli trends at 17 per cent of 56 sites and 0 per cent declining," she said. "The Manawatu River, which is often thrust into negative limelight, is showing a 19 per cent improvement for E. coli."
The results will also be on the Land, Air, Water, Aotearoa's (LAWA) new 'Can I swim here?' website.
Mr Gordon said he hoped the scheme would reinforce that most of the region's popular swimming spots were safe.
"We also hope it will dispel some of the myths, such as that rivers should be swimmable 100 per cent of the time. Unfortunately natural occurrences, such as high flows and floods, means this will never be the case.
"Water quality is just one factor in a number of potential health risks. We ask the public to be aware of hazards such as unstable banks and cliffs, submerged logs, and tsunami warnings and rips at beaches."
He also reminded the public samples may not be reflective of the entire week's water quality.
"A general rule is if the water looks clear and it's three days after rainfall, you should be good to go."