MfE, NIWA wade into clean water debate with fresh data

Two reports released Thursday May 11, by NIWA and the Ministry for the Environment on the technical background to the Clean Water proposals in an effort to clarify the Ministry for the Environment’s (MfE) plans to clean up New Zealand waterways.

The grading system posited by MfE’s Clean Water Plan has generated significant debate. The latest reports have been compiled in an effort to provide broader context on how the grading system compares internationally and the level of precaution they are based on.

According to MfE, the reports provide more detailed information on the levels of risk from swimming in the different grades of rivers and lakes. The average infection risk when a person makes no assessment of the state of the waterway before swimming is rated at 1 per cent for the blue category, 2.4 per cent for the green category and 3.1 per cent for the yellow category. If a person follows the advice of not swimming during high flows, determined as three times normal flows, the risks drop to 0.3 per cent for blue, 1.3 per cent for green and 2.0 for yellow.

“These reports show that the only other jurisdiction that attempts to grade waterways for swimming is Europe. Their grades of excellent, good and sufficient match the New Zealand grades of excellent, good and fair, although the New Zealand proposals for the bottom fair category are more cautious.  This analysis shows that if New Zealand adopted the European grading, more rivers would be deemed swimmable”, noted Environment Minster Nick Smith.

MfE is inviting further submissions from water quality scientists, and others with an interest, on the details of the gradings outlined in these additional reports by 25 May.

The reports can be viewed and downloaded at:



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