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Is it Safe to Swim?

Is it Safe to Swim?

During summer, Wellington’s regional, city and district councils monitor the quality of water at popular beaches and rivers each week. Toxic algae, which can be dangerous for dogs, is also monitored at river sites.



Water quality alerts

Check our interactive alert map for the latest information.

If you notice a problem with water quality then you can report it to us on 0800 496 734.

How do you know if it is safe to swim?

Our water quality in the region is usually very good, but there are a few things to keep in mind before you dunk your head under. Especially if you’re a dog!

Wait for two days after rain before you swim again

Water quality in our rivers and at our beaches is generally pretty good over the summer, except in poor weather conditions.

Heavy rain flushes contaminants from urban and rural land into waterways and we advise you not to swim for at least two days after heavy or prolonged rain – even if a site generally has good water quality.

Find out more about swimming after rain.

Toxic Algae

Toxic algae (known scientifically as cyanobacteria) are an ancient group of photosynthetic bacteria. In summer, the Hutt River regularly has high levels of toxic algae. Toxic algae is only an issue if you eat or swallow it. It is still safe to swim when it is present. It poses the biggest threat to dogs. 

The algae forms leathery looking mats on rocks in the riverbed, and ranges from blackish/brown to dark green in colour (it's quite different from normal harmless green algae, which looks bright green and often forms long strings). These mats can come loose and wash up on the edge of the rivers, or form ‘floating rafts’ in shallow areas. As they dry out they turn light brown or white and produce a strong musty smell. This is when it poses the biggest risk to our dogs. They love the smell and many dogs will try to eat it if they get the chance.

The algae produces a powerful neurotoxin that is very dangerous to dogs if they eat it. In extreme cases, dogs can die within 30 minutes after the first signs of poisoning.

The best thing you can do to keep your dog safe is to know what toxic algae looks like and avoid it. Check our monitoring information for a heads up where algae may be at dangerous levels. If in doubt keep your dog on a lead.

This video shows you what to look out for:


Toxic algal mat growing on the river bed

Toxic algal mats washed up on the river's edge

Henley Lake in Masterton often has high levels of toxic algae and we recommend you don't let your dog swim in or drink from this lake.

Find out more about toxic algae

National water quality trends and data

If you are travelling outside of the Greater Wellington region you can find water monitoring information from around the country on LAWA. LAWA is a key resource for measuring the current state of New Zealand's waterways and shows longer-term trends, information and data.