How water quality at Whanganui's swim spots stacks up

Swimmers arrive at the Union Boat Club pontoon in the Bridge to Bridge Swimming Race. Photo / file

Whanganui's sea swimming has been good this year - but water quality in some of its rivers and streams can be poor.

The situation concerns Horizons Region councillor Nicola Patrick, who has taken her children swimming at Lake Wiritoa and in the Whanganui River at the Union Boat Club pontoon.

Both those places are ranked green for swimming suitability by the Land,Air, Water Aotearoa (LAWA) website - the best source of information about water quality.

Not so good are the three west Whanganui streams: Ototoka, Kai Iwi and Mowhanau.

They have had poor or special status since 2019.

The Kai Iwi is suitable for swimming 16 per cent of the time, and the Mowhanau 11 per cent of the time, according to LAWA.

The Western Whanganui Catchments Incorporated Society is working to improve the situation.

"Even though we have got people getting a lot more active and we have got a campaign we know it takes time to start shifting stuff," Patrick said.

The main contributor to poor swimming water quality is rain washing animal effluent into waterways off land that is poorly managed and has no riparian fencing or planting.

But substances from wastewater treatment plants and septic tanks also contribute, and Horizons Regional Council has monitoring in place and programmes to improve the discharges.

Even excrement from birds like ducks can make a difference.

"You can get red results from a combination of things that aren't the headline grabbers," Patrick said.

The water at Lake Wiritoa gets a green light for swimming at present, and Patrick had no hesitation about her children swimming there provided they avoided surface scum near the lake outlet.

Dudding Lake, however, has elevated levels of the faecal coliform E. coli bacteria.

Swimmers should be cautious there, LAWA says, especially if they are prone to allergies or illness.

Whanganui's sea beaches are generally suitable for swimming at least 70 per cent of the time - for Ototoka that's 98 per cent, and Kai Iwi 88 per cent.

The Whanganui and Rangitikei rivers are also mainly swimmable - though not in the three days after heavy rain and swimmers need to watch out for logs and currents at any time.

The Whanganui River at Pipiriki is only suitable for swimming 65 per cent of the time - 30 per cent of the time it's unsuitable.

The Manganui a te Ao, with a prime swimming spot at the Ruatiti Domain, is only suitable for swimming 82 per cent of the time.

For the Makotuku River at Raetihi's campground it's only 53 per cent of the time, and the Moawhango River at Moawhango is rated unsuitable now.

Its E. coli levels have been "outrageous" at times, Patrick said, and are currently above the 540 level that makes swimming unsafe. Its toxic algae level is also high.

"That's one I will definitely be looking into," she said.