Thorough analysis of our waterways essential if we’re to preserve our blue economy.

Look at those extraordinary images of the Earth from outer space and you'll see that our beautiful islands lie at the heart of the world's largest ocean.

We live in a blue, watery world and, along with the land, the state of our rivers, lakes, groundwater, estuaries and harbours are fundamental to Kiwi health and prosperity, now and in the future.

Much of our wealth is generated from waterways and the ocean. It would be interesting if our universities followed the lead of the University of Michigan, sited near the largest source of freshwater on Earth. Their economists and scientists have analysed the contribution of the Great Lakes and its linked network of rivers to the state and national economies, and the results were impressive - almost a quarter of the region's payroll depended on these waterways.

In New Zealand, a robust analysis of the contribution made by rivers, aquifers, harbours and the ocean - the blue economy - to our national accounts is needed urgently. I think the results would convince even the most died-in-the-wool sceptic that degrading or destroying our rivers, aquifers and harbours is the act of a masochist or fool.

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At an Environmental Defence Society strategy (EDS) conference in Auckland recently, Niwa scientist Dr John Zeldis gave a presentation about the current state of the Hauraki Gulf that brought me up with a jolt. His meticulous data, collected over the past 15 years, showed a steep rise in dissolved inorganic nitrogen (DIN) in the gulf. This leads to eutrophication, the process that generates algal blooms and destroys oxygen and life in harbours, rivers and lakes.

According to the UN Environmental programme, eutrophication reduces biodiversity and creates toxins dangerous to humans and animals. By far the greatest source of DIN in the Hauraki Gulf comes from the Waihou River, which has been affected by the intensification of agriculture over the past few years, without proper attention to impacts on the state of groundwater and our waterways.

How many of us realise that our enjoyment of the Hauraki Gulf depends on the state of the Waihou River? Until the conference, I didn't.

There is no room for complacency. Some years ago Chesapeake Bay, the largest estuary in the US, experienced an ecological collapse. Apart from the impacts on fisheries, swimming and other marine sports, what would happen to New Zealand's largest city, our "clean, green" image, tourism and the national economy if the Hauraki Gulf suffered a similar fate?

That is why we have to act decisively. Our waterways are a terrific "canary in the cage", telling us about the impact of land use patterns and farming systems on rivers, aquifers, groundwater, lakes, estuaries and harbours, and on our own health, wellbeing and prosperity - even survival. When our rivers, lakes and estuaries start dying, we should be very worried indeed.

Thinking about the blue economy and the vital role our waterways play in creating wealth helps to bridge the gaps between land, freshwater, the sea, the atmosphere and human communities, and scientists who try to understand them.

A blue economy would aim for abundance, not sustainability, and harness all our efforts to make this possible. We want businesses, communities and ecosystems to flourish together, and there are smart ways to make this happen. At the EDS conference, for instance, the mayor of Copenhagen shared ingenious strategies for managing urban water while enhancing ecosystems, which were infinitely cheaper than hard engineering solutions. Auckland City could use some of these clever ideas.

As for telling Kiwis that they have to choose between dirty rivers and cellphones, forget it! We are not that stupid, and deserve better. The vast majority want clean, healthy rivers for our children and grandchildren to swim in. We need to stop chasing the quick, dirty bucks and take care of our waterways, the source of lasting prosperity and the lifeblood of the land.

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Dame Anne Salmond is patron of the Te Awaroa 1000 Rivers Project.