New research by Kiwi scientists has revealed pristine lakes around the world - including Queenstown's Lake Wakatipu - are degrading at an "alarming" rate due to the growth of bright-green slimy algae.
The research was co-led by scientists at Nelson's Cawthron Institute and explored the potential causes of the algal blooms such as nutrient pollution, climate change and the loss of animals that eat the algae.
The findings were published in BioScience Magazine this week.
It found pristine lakes around the world are being carpeted by bright-green slimy algae growing on the lake bed, especially during the summer - a phenonemon that is "deeply concerning" to scientists.
Cawthron Institute scientist Dr Simon Stewart said typically, when a lake experiences degradation, the water becomes enriched in nutrients and filled with algae, but some of the lakes they studied which have algae mats growing on the lake bed have clear water that is free of nutrients.
"The fact these blooms are occurring in essentially pristine lakes is an indicator that freshwater ecosystems are rapidly changing and the blooms could be early-warning indicators of ecosystem change, but we have a puzzle to solve because traditional monitoring methods can't tell us much about the problem," he said.
Dr Stewart said there are several lakes in New Zealand that are already experiencing the algae blooms, including Ōtūwharekai near Ashburton, Lake Wakatipu in Queenstown, and Lake Taupō.
"Our team have been sampling and monitoring these blooms in a few lakes in New Zealand, including Taupō, to shed light on what is driving these blooms.
"But unlike the offshore waters in lakes where in some instances monitoring data goes back 100 years - and the theory is well-established, we're starting from a fresh slate so we're having to work smarter.
"This is why the global research partnership is so important - by sharing knowledge and resources with partners worldwide we can all make progress together."