The Manawatu River is one of the most polluted in the western world. It is unsafe to swim in or drink from. In places, it smells like burnt sheep and faeces. Its easy to despair when you read reports like that. But it doesn't have to be that way. And looking overseas, the tale of the Thames shows that rivers can be cleaned up:

 

   Filthy, opaque and stinking of rotten eggs: this was the River Thames of 1957. Declared biologically dead thanks to its soaring pollution levels, Britain's most famous waterway was paying the price for decades of human use – and not for the first time. Since the 18th century, it has been a hotbed of industrial activity; during the "Great Stink" of 1858, the stench of human waste along the riverbanks forced Parliament to drench its curtains in chloride of lime and almost prompted the city's law courts' evacuation to St Albans.

    A century and a half later, things look rather different. With 125 different species of fish navigating its curves, 400 invertebrates wallowing in its mud, and a selection of seals, otters and dolphins to be spotted, the Thames has achieved a transformation of staggering proportions. Eighty per cent of the Thames is now judged to have "very good" or "good" water quality, while the past five years have seen almost 400 habitat enhancement projects and more than 40 miles of river restored.

In the case of the Thames, that didn't come about from a single, co-ordinated effort - just from the gradual tightening of standards over the years. We can, and should, do the same here.