Kiwis are being warned to do their due diligence before taking a dip this summer, as poor water quality threatens many of the country’s waterways.

Troubling trends have emerged over recent months, with two-thirds of rivers rating poorly for harmful E. coli and 60 percent of lakes found to be breeding grounds for algae.

The data was collected by the Land, Air, Water Aotearoa (LAWA) project, which takes water samples from 850 popular rivers, lakes and beach swim spots.

Those samples are then tested and results available through an interactive map on its website.

Lawa science lead Ana Madarazz-Smith told Newsable safe and unsafe spots often sit side-by-side.

“Sometimes lagoons can have a lot of bird life, be warmer, and bacteria loves that warm, slow flowing water, and that’s right next to a beach, [which has] really high energy, clean water coming in and out”, she said.”

“You can have them in quite close proximity.”

Madarazz-Smith added that it’s difficult to “identify trends” in water quality because there’s so much variability.

“You want to be able to go… I’m thinking of heading to X spot this weekend… What are some of the things that I should be looking out for using that safe swimming checklist?”, she said.

Check out the “Can I swim here?” map to learn more.

Listen to the full interview here.

Newsable is Stuff’s daily news podcast, wrapping up what’s worth talking about in a short package every weekday morning. Make sure to like and follow us wherever you get your podcasts and across Instagram and TikTok.