Rivers at risk

New Zealand's freshwater treasures are degraded by more than just forestry.

- Andrea Graves

There's a lot of slash anger about. It's directed at forestry companies and the regulators that allow them to leave behind large quantities of tree trimmings, which are washed down rivers to the coast during severe weather events, causing devastation.

Forestry has been described as the only sector that gets to internalise the benefit and socialise the cost. But that tactic underlies the profitability of several sectors. One externalised cost that's rife is freshwater pollution. It harms the water's occupants native freshwater fish, insects, kakahi (mussels) and kōura (crayfish) - mostly slowly, but sometimes catastrophically.

When land is cloaked with trees, even pine, waterways are largely protected. But when trees are fertilised, and during harvest and for a few years afterwards, waterways can receive harmful runoff. Agriculture inflicts the same problems on many more waterways. Urban runoff is also an intense polluter, although fewer waterways are affected.