New Zealand’s water has taken a massive hit in areas of urban settlement and pastoral farming.
There are many causes including: cutting down forests; introduced pests and plants; disposal of human sewage; removing water for irrigation and electricity generation; industrial discharges; urban stormwater; the drainage of wetlands and farming practices.
Depending on local conditions, it may take decades to see the impacts of current practices on water quality.
Over the past two decades most measures of water quality have been declining. More recently some of those measures have started to stabilise and a few have improved. This is probably because farmers have fenced and planted some rivers, keeping their stock out. However, indicators of ecosystem health still show a worsening trend.
In recent decades the impact of human sewage and industrial waste has reduced. This leaves the increased intensity and coverage of dairy farming as the most likely cause of any continuing problems. There has been a substantial change in land use, especially in some regions, from low intensive sheep and beef farming to highly intensive and irrigated dairy farming.
Why are cows a problem? More cows means more urine going onto the land, which means more nitrogen leaching into our waterways.