Some of the world's clearest lakes are under threat from algae

A microscopic algae called Lindavia -- which causes a sticky mucus-like substance known as 'lake snow' -- has been found in Lake Rotoiti and Lake Rotoroa at Nelson Lakes National Park.

The algae isn't toxic for humans, but the the mucus substance takes away from the lakes' pristine conditions.

DOC Community Ranger Sandra Wotherspoon says the "lake snow" hangs under the water and can be a nuisance by sticking to fishing gear, boats and people.

She's asking visitors to check, clean and dry any clothing that comes into contact with the algae.