Whanganui swim spots get mixed rating

Mowhanau stream had a 50 per cent red light status for water quality this week. Photo / Bevan Conley

Natural swimming locations in Whanganui continue to be too toxic to swim in, prompting Mayor Hamish McDouall to call for "urgent" considerations around land use.

The Ototoka, Kai Iwi and Mowhanau streams were given a long-term special status in December 2018 because of their poor or highly variable water quality.

This week the Land, Air, Water Aotearoa (Lawa) website gives each of them 50 per cent amber status (caution) and 50 per cent red light status - no go.

They are high in the E. coli faecal coliform bacteria, as well as nitrogen and phosphorous.

The Whanganui West Catchment Group is working to improve them.

The coastal streams are special places for recreation, McDouall said.

"Those streams should be clean enough not just to swim in, that's the lowest standard, but clean enough to bring back the wairua, the fish and the ecosystem.

"I hope it will lead to urgent considerations around land use," he said.

Last week was warm enough to tempt swimmers into the water - but swimming is not advised at several other popular freshwater spots.

The warm weather drove up the density of potentially toxic algae at Dudding Lake. It got a red light warning from Lawa.

The warning is based on a sample taken by Horizons Regional Council on November 8, at the start of a week of unseasonably warm day and night temperatures.

The lake reserve is popular for camping, boating and swimming. Operator Bruce Gordon said the swimming no-go so early in the season was annoying.

Usually, algal density doesn't build up to risk levels until the first week of December. He's not too concerned because he expects algae levels to drop when temperatures fall and winds increase.

The grass carp and freshwater mussels in the lake will improve its water quality long term, he said.

Algae levels are up at Whanganui's Lake Wiritoa too, prompting an amber light and a warning to swimmers to be cautious.

Both lakes have been closed by algal blooms in past summers. People using them are advised to avoid surface scums and water that looks very green.

Swimming in the Whanganui River at Pipiriki is also not advised, because of high E. coli levels.

Whanganui's other top swim spots get the Lawa green light for swimming this week. They are the Whanganui River at Mosquito Point, the Union Boat Club and the Town Wharf, and South and Castlecliff beaches.

Horizons Regional Council takes weekly water samples at more than 80 swim spots in the region from November 1 to April 30. The results are shown on the Can I Swim Here? section of the Lawa website.

It provides a map where people can click on swim spots and get the latest test results as well as the long-term outlook.