Popular swim spots in the region were swimmable for the majority of last summer, Horizons Regional Council reports.
Horizons conducts weekly water quality monitoring at 26 popular swimming spots from November to April every year. The results of this monitoring were reported at the council's June environment committee meeting.
The term "swimmable" is determined by a number of factors, such as bacteria levels, whether cyanobacteria are present, and flow, Horizons group manager natural resources and partnerships Dr Jon Roygard said.
"It's not as simple as making a general comment that a river is swimmable or not - what we are really looking at is how often it is safe to swim," he said.
"From a Ministry of Health point of view, if the site has under 550 E.coli per 100ml then it should be swimmable.
"We are pleased to report that most of the region's coastal swimming sites were safe to swim for the entire summer."
Neither of the exceptions, Hokio and Waikawa beach, were near Whanganui.
Popular freshwater spots also recorded well.
Dr Roygard said the portion of time that swim spots were not suitable for swimming was due to rainfall and high flows.
"During high rainfall bacteria and sediment naturally washes from the land into our river systems. This results in high flows which makes some sites potentially dangerous, and people wouldn't likely choose to swim during this time.
"The good news is that during the warmer and drier months our reporting shows swimming spots are often well within the Ministry of Health's swimmable standards."
The monitoring programme also provides the council with robust information on where E.coli levels are high in the region and where they can focus their efforts.
"We realise there is always room for improvement."
Work is also under way through initiatives such as the Sustainable Land Use Initiative to improve water quality and reduce sediment run-off.
"A key focus of this work has been improving suitability for swimming by reducing the amount of bacteria getting into the river from discharges and completing stream fencing," Dr Roygard said.
-The report is available for viewing at the council's website, horizons.govt.nz