The cost of irrigation

At the moment, the government is pushing irrigation and water storage as a way of increasing milk production and boosting the economy. Critics have argued that the result will be dirty, polluted rivers unfit for recreational use. And we've just been handed the perfect example. In the 90's, a major tributary of South Canterbury's Opihi River was dammed for irrigation purposes. 15 years on, whitebaiters have been forced to abandon the river because it is so polluted:

Whitebaiters are giving up on the Opihi River because of high levels of algae.

Timaru man Brian Bennett has been fishing the river for almost 70 years. After leaving his net in it for 15 minutes yesterday, he found it covered in algae. "It's the worst I've ever seen."

Bennett said the problem had worsened in the past five years, despite an improvement in 2013.

Fellow angler and whitebaiter Des Thomas, who has given up fishing in the "black, filthy" river, said he "wouldn't eat it [whitebait] if I caught it" in the Opihi.

He believed a combination of the Opuha dam reducing water flows and rising nutrient levels had allowed algae to thrive in recent years.

This isn't a one-off incident; its been going on for years. And the major culprit is the dam blocking "flushing flows". It could of course release them manually, but that's water which could be sold to farmers and turned into cowshit, so they won't.

The upshot: irrigation ruins rivers. Rather than encouraging it, the government should be restricting it to protect our environment and recreational values.