Decision 17: Bill English stands by Oreti River swim comments

In the Newshub Decision 17 debate, National Party leader Bill English said he'd still swim in his childhood river, the Oreti in Southland.

On Wednesday on the campaign trail in Southland Bill English stood away from the river, but stood by his claim.

But experts say the Oreti is one of the country's most degraded waterways. So is it is safe to swim in or not?

Where the Oreti River meets the sea, it's sludge. The area used to be abundant with cockle beds, but now they're gone, suffocated by silt.

Government figures show the Oreti's quality is excellent at its headwaters, fair at Dipton and poor in the lower reaches. The river's quality decreases as it passes through dairy farming country.

Six sites in Southland were deemed too dangerous for swimming by the Ministry for the Environment report last summer - including one of the swimming holes near Dipton.

A 2016 report by UC, Uni of Waikato and independent science organisation the Cawthron Institute on the spread of harmful algae Cyanobacteria found 103 waterways had algae covering more than 20 percent of their river beds. It proliferates as a result of nitrates and fine sediment - caused by dairying.

And the river with the highest concentration was the Oreti.

But Dipton farmers are backing Mr English, and so too are locals.

River quality - dividing opinion in the south, and in this campaign.