Can I swim here? Check the water quality before you get in

A man in the ocean throwing a happy baby up in the air.

We monitor over 100 sites around Canterbury for water quality

Waitaha/Canterbury has some stunning swim spots to cool off during hot summer days, but it’s important to be aware of water quality issues and how to stay informed.

Before heading to the beach, river or lake to swim, visit the Can I Swim Here? section of the Land and Water Aotearoa (LAWA) website, and look for water quality signs when you’re there.

Over the summer we monitor more than 100 popular swim and recreation sites in Waitaha/Canterbury to check for bacteria (E. coli and enterococci) as well as potentially toxic algae (cyanobacteria) that might be harmful.

Our monitoring programme

Sites are monitored weekly from November to March. As water quality can change, it’s best to check the LAWA website for up-to-date information so you can make informed decisions about where’s best to swim.

We grade each site on its suitability for recreation based on the last five years of data from bacterial sampling.

For sites graded fair or better, if our weekly result shows the water has changed and may be unsuitable for recreation, Te Whatu Ora’s National Public Health Service will issue a health warning for that site, which will be listed on our Health Warnings page and the LAWA website.

The sites that are graded poor and very poor are not recommended for swimming because there is an elevated risk of getting sick. We will continue to monitor those sites, but health authorities do not issue health warnings as permanent signage should be erected at the site by local councils.

Key grade changes

Changes this year to sites where suitability for recreation has degraded to poor or very poor include Corsair Bay, Diamond Harbour Beach, Rāpaki Bay, Purau Bay, Akaroa Main Beach, Waipara River at Boys Brigade Swimming Hole, Te Waihora/Lake Ellesmere at Lakeside domain, and Pareora River at Huts.

Our surface water science team leader Shirley Hayward said that many of the coastal harbour sites were affected by rainfall events last summer. "Heavy rainfall can sometimes cause increased runoff of faecal bacteria into our water.

"We plan to investigate the sources of bacteria with additional testing over the coming summer," said Hayward.

Avoid swimming after rain

Swim sites can be affected by rainfall, especially those with fair or poor grades. It’s important to avoid swimming for 48 hours after rain.

"This is because of the increased risk of faecal bacteria in our waterways after rainfall. Even if the water looks clear, it doesn’t always mean the water quality is good to swim," said Hayward. 

Sources of faecal bacteria can include animals (birds, dogs, livestock) or wastewater overflows into the stormwater network.

Potentially toxic algae - know what to look for

Slimy benthic cyanobacteria on a rock

Benthic cyanobacteria grow on the bottom of river beds

Potentially toxic algae (cyanobacteria) are naturally occurring with the potential to bloom and may produce toxins that can harm people and pets.

Blooms form when cyanobacteria grow quickly, usually due to changes in environmental conditions such as warmer temperatures, sunlight, high levels of nutrients, or stable river flows.

"Unfortunately, dogs love the musty smell of potentially toxic algae and are naturally drawn to investigating it – usually by licking or ingesting the material. It can be quick acting and fatal to dogs," said Hayward. "The best way to protect yourself, whānau and pets is to know what potentially toxic algae looks like and avoid it.

"This is because small amounts of potentially toxic algae can be present in a waterway that is listed as good for people to swim, or you may be visiting an unmonitored area."

In rivers, benthic cyanobacteria grow on the bottom of riverbeds. It appears as thick dark brown or black mats that have a slimy or velvety texture and a strong musty smell. These mats can detach and gather at the river’s edge. 

In lakes, ponds and lagoons, planktonic cyanobacteria are suspended in the water. Water can look cloudy, discoloured, or like it has small globules in it.


For people
Faecal pathogens (such as bacteria and viruses) can cause gastrointestinal illnesses (including diarrhoea and vomiting); respiratory diseases; and eye, ear, nose, throat and skin infections. Symptoms of cyanobacteria toxin poisoning in humans include tingling or numbness around the fingertips and/or mouth; breathing difficulties; gastrointestinal symptoms and skin rashes.

Read more about the health risks associated with contaminated water.

For pets and livestock
Symptoms of cyanobacteria toxin poisoning in animals include panting; lethargy; muscle tremors; twitching and convulsions. If you are concerned, contact a veterinarian immediately. You or your vet can report to us any animal illness resulting from contact with cyanobacteria.

If in doubt, keep out

Before you go, make sure you keep in mind:

  • Check the water quality on LAWA
  • Avoid swimming for two days after heavy rain
  • Follow any warning signs
  • Know how to spot potentially toxic algae and avoid it
  • Avoid eating shellfish from areas where health warnings are in place
  • Check for hazards

If you have any doubts about the water quality, it’s best to be cautious and avoid the water.

We’ll be sharing some top tips on where it is good to swim during summer via our Facebook page so keep an eye out for swimming inspiration.