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Is it safe to swim?

Is it safe to swim?

Summer is a great time to enjoy our coast and waterways, but there are some times and places where caution is needed. The best thing you can do to keep safe is to know what toxic algae looks like and avoid it.

Toxic Algae

When the weather is dry our rivers can produce toxic algal blooms, especially where the water is already shallow. We monitor the toxic algae in rivers in the region, and work with councils across the region to keep river and stream users informed. 

The algae grows on submerged riverstones in a shiny brown/dark green coating. When it dies it floats to the surface and forms small brown mats at the water’s edge. It is important to keep an eye on babies and toddlers who are inclined to put objects in their mouths. Seek emergency medical attention if anyone in your group swallows toxic algae.

If you have been swimming in a river or lake and you have any of the following symptoms: nausea, vomiting, numbness, tingling, muscle twitches, shaking, weakness, breathing difficulties and potentially convulsions and loss of consciousness see your doctor immediately.


Dogs are at greatest risk from toxic algae because they love the smell of it and will eat it if they can. During a bloom, they must be kept on a leash along the river bank. If you suspect your dog has eaten even a small amount of toxic algae (coin sized) take it straight to the vet.

Greater Wellington is monitoring popular swimming spots weekly throughout the summer. We will issue an alert if toxic algae reaches unsafe levels, but please learn to recognise and avoid it.

Toxic algae in depth

Tummy Bugs

Stormwater entering our rivers brings with it a small amount of waste from animals (such as birds and dogs) and sometimes untreated human sewage from overflows. This can be a significant health risk after heavy rain. Only swim when the water is clear – this applies to rivers or the sea – and wait for 48 hours after heavy rain. Another good guide is “can I see my feet when I’m standing up to my knees in the water?”

Our water quality map shows the overall water quality at 85 sites around the region. It is updated weekly from 1 December – 31 March. If you notice a problem with water quality you can report it on 0800 496 734.

Learn more

Toxic Algae levels are high in the Hutt River, upstream of Silverstream bridge. We advise against swimming in that section of the river, and that you keep your dog on a leash if walking nearby. Birchville, Maoribank Corner, and Poets Park also have new growth, though at lower levels.