Ninety per cent of farmland upstream from Whangarei Falls remains unfenced, with one district councillor saying more needs to be done to clean up one of the district's flagship tourist attractions.

Microbial Source Tracking (MST) that Northland Regional Council carried out in March 2010 tracked the species responsible for faecal contamination and found wildfowl the likely culprit. However, this was in the midst of Northland's worst drought in 60 years, meaning farm surface runoff was not accounted for and more recent results point the finger back at farm animals.

Whangarei District councillor Tricia Cutforth is on NRC's Environmental Management Committee and said the "softly softly" approach to farmers who neglected to fence their land had gone on long enough. She said she had always found it hard to believe that birds were responsible for the pollution. The swimming hole at Whangarei Falls exceeded safe e.coli guidelines in 36 per cent of the weekly samples last summer, and 18 per cent so far this year. There were permanent signs warning people the swimming hole was regularly unsafe to swim in.

"Here it is, supposedly a jewel in our crown and certainly on the visitor radar, with local people swimming there with signs saying don't swim - and tourists seeing this," she said.

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Further MST testing in July 2015 near Vinegar Hill Rd found farm animals were mainly responsible for water contamination there. NRC group manager regulatory services Colin Dall manager said the 2010 results may have been influenced by drought.

"However, faecal material from ruminant sources can still enter water during periods of dry weather via direct discharges from animals standing in or near waterways or from effluent treatment systems that discharge to waterways."

Record low rainfall levels were recorded between November 2009 and April 2010 and Mr Dall said no rain was recorded in the period before the sample was taken. About 30 per cent - or 29km - of the waterways that fed the falls were on pasture land. Of these, 90 per cent did not have stock exclusion fencing.

An upper Hatea River Catchment working group, which included representatives from NRC, Whangarei District Council, Northland District Health Board and community groups, would go on a field trip this month to get a further grasp of the problem, Mr Dall said. He said possible solutions discussed had included environment fund grants for fencing, more signs and "awareness raising".

NRC figures show that 65 per cent of the more than 900 farms inspected over four months from mid-August last year had achieved full compliance.