Fencing of waterways an effective tool to combat pollution
Fencing of waterways has proven very effective where it has been used to combat the risks of contamination from
agriculture, AgResearch says.
AgResearch’s Professor Rich McDowell, the chief scientist for the Our Land and Water National Science Challenge, was
speaking after the publication of a study looking at policies for fencing waterways on contamination loads in New
His paper was published in the American Journal of Environmental Quality.
The Ministry for the Environment’s Our Freshwater 2017 report indicates that urban waterways have the worst overall
water quality in New Zealand, but much of the public focus in recent years has been on the impact of agriculture -
particularly dairy farming - on waterways in rural areas.
“Fencing is very effective at reducing contaminant loads to waterways - by 10 to 90 per cent depending on the nature of
the contaminants and local issues,” Prof McDowell says.
“Fencing works especially well for the likes of E. coli or phosphorus contamination that can result from animal wasteor stream bank destabilisation. However, fencing all
waterways in New Zealand is impractical and in some places other good management practices may be more cost-effective.”
“A combination of better awareness of the issues and the use of good management practices (including fencing) in the
right place is starting to reverse degrading trends in the likes of phosphorus and sediment in the water over the last
decade,” Prof McDowell says.
Dairy farmers had invested in a major programme of fencing waterways to the equivalent of nearly 27,000km. They should
continue to do so as it is effective at reducing waterway contamination, Prof McDowell says.
“The fact that most of the contaminant load comes from areas not requiring fencing reflects the much greater number and
areas occupied by small streams – potentially from steeper country where dairy farming is unlikely to be present. Other
work also indicates that a substantial proportion of contaminant concentrations may be from natural sources.”
AgResearch Research Director Greg Murison says there is a big focus by his own organisation and others, including
DairyNZ, to support farmers in developing management practices that reduce the risk of water contamination.
“The number of science programmes looking at these issues demonstrates how scientists are being responsive to what is
important to New Zealanders.”