Millan Ruka, from Environment River Patrol Aotearoa (ERPA), hosted the Greens' river ride. Following the trip, Ms Delahunty visited Northland Regional Council (NRC) and dropped off at Whangarei District Council's Water Testing Laboratory a sample of water collected near an effluent pond's discharge into the river.
The results are due next week.
Ms Delahunty said she was pleased to see more riverbank was fenced than during a previous visit to the Wairua River but a stretch of unfenced farmland clearly showed the damage dairy or cattle were doing.
"There's definitely an improvement in the fencing but the water quality looked murky, really polluted."
The Our Fresh Water report measured water quality, quantity and flows, biodiversity and cultural health in samples sites throughout New Zealand, although a regional breakdown is not yet available.
It showed urban waterways were the most polluted, with levels of the harmful bacteria E.coli 22 times higher in urban areas but nearly 10 times higher in pastoral rivers, compared with rivers in native forest areas.
Ms Delahunty said the National Government had failed to protect New Zealand's fresh water systems and was trying to "pull a fast one" by raising the allowable level of bacteria in rivers and lakes so they conformed to a new "swimmable" standard.
She said the NRC was in a similar position to similar authorities where the government expected it to do more with limited resources. Nor was the NRC responsible for the Government's "weak'' water standards.
Ms Delahunty said while Northland had water quality problems due to land use, "it was not as bad as in some parts of New Zealand''.
Secretary for the Environment Vicky Robertson said land use had clearly affected the state of fresh water but a recent strong focus on how swimmable the waterways were was just part of the story. She described the situation as "critical".
The new report has landed in the public arena only a day before submissions close to the Government's new Clean Water Package.
The Wairua River is the most northern of 10 rivers in New Zealand the Green Party picked last year for its "swimmable rivers" campaign.
In Whangarei last night, Ms Delahunty and Mr Ruka spoke at a public meeting on the health of the Wairua River and presented Green Party solutions to protect water quality.