Freshwater is one of New Zealand's key strategic assets.

It is why we are so good at growing food. It is pivotal to our clean green tourism brand. It is part of what makes for our great Kiwi lifestyle.

The management of water has historically been left to councils with little direction or monitoring from Government. We started changing that in 2009 when we required councils to progressively meter water takes.

You cannot manage what you don't measure. We introduced the first National Policy Statement on Freshwater in 2011 that requires councils to set minimum flows in our rivers. In 2014 we added requirements for councils to limit pollutants.

We also passed a new Environmental Reporting Act in 2015 so there is open, independent reporting on the state of our waterways.

We are currently consulting on the next steps. This includes a plan to achieve 90 per cent of our rivers and lakes being swimmable by 2040, a national regulation requiring stock to be excluded from waterways, tougher requirements for limiting nutrients and a further $100 million to help fund clean-up initiatives.

A credible national plan for improving water quality for swimming requires a consistent grading system so we can set clear targets and monitor progress. This is difficult because even our cleanest rivers can become badly polluted during heavy rainfall.

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Water quality scientists from NIWA have developed a system that applies five colour grades based on the proportion of time a river meets swimming water quality standards, ranging from blue (excellent; suitable for swimming >95 per cent of the time), green (good; 90-95 per cent), yellow (fair; 80-90 per cent), orange (intermittent; 70-80 per cent) and red (poor; <70 per cent).

This has been applied to the 45,000 kilometres of rivers large enough to swim in (more than 40cm deep) and the 9000 kilometres of margins of lakes which are greater than 1.5 kilometre in perimeter.

Maps across the country tell a powerful story of where it is safe to swim and where communities need to lift their game to improve water quality (See www.mfe.govt.nz).

The plan requires the blue category be increased from the current 41 per cent to 50 per cent, the green from 15 per cent to 20 per cent and the yellow from 16 per cent to 20 per cent, increasing the total suitable for swimming from 72 per cent to 90 per cent.

The plan also requires the proportion of polluted rivers graded orange to decrease from 16 per cent to 8 per cent and those graded red from 12 per cent to 2 per cent. This requires improvements in water quality for 26,000 kilometres of waterways by 2040, or 1000 kilometres per year, moving to a cleaner category.

Achieving these improvements in water quality will require more than $2 billion of investment. The Government has already committed $350 million to help fund improvements with a further $100 million currently open for applications.

The plan comes with national regulations requiring farmers to fence dairy cows, pigs, cattle and deer from waterways at a cost of $370 million. It will also require significant upgrades by councils of wastewater and stormwater infrastructure.

The timeframe has been criticised by some as too slow. It has taken a century of land clearance, urban development and farm intensification to degrade our rivers and lakes.

Those responsible for implementing the plan like councils are worried it's too ambitious.

One Green MP damned the water quality measure because it suggested rivers were swimmable when the flows could be too high or too low. People still need to apply common sense and make judgements about safety relative to flow rates.

Other critics say the only way to achieve clean water is to cease the farming of livestock without any regard for the economic consequences. Another MP wanted government to require our waterways be drinkable all of the time even through this has never happened in the past.

These impractical demands should not divert us from the challenge of making our rivers and lakes cleaner.

The commentary on water quality too often assumes it is just an issue for farmers. The science shows that the average E. coli per 100 millilitres ranges from 20 in waterways adjacent to indigenous forests, 67 in exotic forestry, 190 in pastoral farming areas and 440 in urban areas. This plan requires everybody to tidy up their act.

The plan is expressed as making our rivers and lakes more swimmable but the benefits are much wider. It will improve our rivers and lakes for kayaking, rafting, fishing, and ecological health.

This is the first national plan that sets specific targets to improve water quality across New Zealand. It is ambitious and will deliver a standard unmatched internationally. It is also practical, science based and affordable.

We welcome feedback on the detail. Our ultimate shared goal is improved rivers and lakes that align with New Zealand's clean, green brand.

Dr Nick Smith is the Minister for the Environment.
Views expressed here are the writer's opinion and not the newspaper's. Email: editor@hbtoday.co.nz