Mixed message on water quality won’t deter people from swimming. And nor, in most cases, should it.

If a map in the Herald this week was an accurate reflection of reality, there would be good reason to exercise considerable caution before swimming at many of Auckland's beaches. The map was riddled with orange dots, signifying that 11 of the region's 63 beaches had been given the worst water quality rating.

Included in that number were popular spots such as Milford Beach, Laingholm and Judges Bay. It is a picture strongly at odds with the largely pristine waters that will invite hundreds of thousands of Aucklanders and visitors to take a dip over the coming few weeks.

The gloomy picture is portrayed on a national monitoring website, lava.org.nz, an initiative of the regional councils, the Cawthron Institute, the Environment Ministry and the Tindall Foundation.

It has been trumpeted by the Environment Minister, Nick Smith, as "part of the Government's programme of improving information on the quality of our environment". The problem is that it is unclear what the data is trying to say.

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It is suggested that at the spots deemed "high risk", there is a risk of 10 per cent or greater of illness after swimming. But this conclusion, based on three years of data, is not designed to represent health risk on a particular day. Indeed, some of the spots had acceptable readings at their most recent check.

What, then, is the website trying to say? That there is a very small risk of swimming at these beaches at the worst of times and none much of the time? It is hardly a message that will deter people from entering the water. And nor, in most cases, should it.

The vast majority of Aucklanders appreciate that beaches may be unsafe for swimming for 48 hours after heavy rain has led to run-off into waterways.

Regular weekly water quality testing carried out by the Auckland Council at all the 63 beaches detects the danger and warning signs are quickly erected.

Most people, if not all, are sensible enough to heed these.

Notably, such instances of high bacteria level readings at coastal beaches are quite rare. That is why an incident at Mission Bay in January attracted much publicity and was regarded as a surprise and a puzzle by council officers.

Normally, the popular beach has no such problems. Indeed, even in this case, the impact was localised. Water at the neighbouring beaches of Kohimarama and St Heliers remained unaffected.

Officials suggested the cause may have been as simple as a dead animal's carcass floating by or someone flushing out the waste system on their boat.

Red alerts are equally rare at the likes of Takapuna Beach and Narrow Neck.

And Long Bay, which draws up to 25,000 visitors on some public holidays, is remarkably resilient. If episodes like that at Mission Bay became a regular occurrence and were mimicked at other popular beaches, there would, rightly, be a public outcry. Aucklanders, quite simply, would not accept lower water quality at swimming beaches whatever the financial problems confronting the council.

The region's coastal beaches are a jewel in the region's crown. The overall quality is good.

Only a very few are ever unsafe to swim at, and there is little to suggest they are deteriorating. That appears to be well understood by the crowds flocking to Auckland's beaches this summer.