It's time a law was introduced to ban farmers from allowing any stock into the country's waterways, the Green Party says.
The call follows the Otago Regional Council erecting signs warning people not to swim at popular swimming spots in Otago's Taieri River, after finding high levels of E-coli, an indicator of faecal contamination.
Green Party water spokesperson Eugenie Sage said it was unacceptable that parts of the river next to the Central Otago Rail Trail were unfit for swimming.
"Good farmers make sure stock are excluded from waterways. Where you've got this faecal contamination, it may be because some farmers are allowing their stock access to the river," she said.
"It's fundamental that we have rivers and streams which are free of stock but we don't have any national rules that require that. We need them."
The tourism industry relied on the 100% Pure New Zealand brand to encourage tourists to visit but having tourists unable to swim in the river after a long, hot day of cycling was falling short of that promotional image, Ms Sage said.
It should be a national bottom line that rivers were fit for swimming, she said.