'White flakes’ that have appeared in Lake Te Anau and Manapōuri were confirmed yesterday (24 May) as the introduced and invasive water flea Daphnia pulex, according to Environment Southland (ES).

The Cawthron Institute advises that this species presents no risk to human health.

However, Daphnia pulex can out-compete native Daphnia species, threatening the broader lake biodiversity by creating conditions for other invasive species to grow.

ES chief scientist Karen Wilson said Daphnia pulex is a known species that has previously been observed in many freshwater systems throughout New Zealand over several decades.

However, this is the first time we have seen such a high abundance of this species in both Lakes Te Anau and Manapōuri.

“Our scientists are working closely with experts at the Cawthron Institute to understand the ecological impacts and implications,” Wilson said.

Typically, Daphnia pulex is barely visible with the naked eye, around 1-5mm. However, the size currently observed is large and can be seen as free-floating white flakes a few centimetres below the water’s surface.

“We expect the high abundance of Daphnia pulex to decline over the next few weeks."

"We will continue to monitor Lakes Te Anau and Manapōuri and investigate Lake Hauroko, Lake Monowai and Lake Mavora to determine if these lakes are also affected.” 

ES has advised that all fishing, boating and recreation equipment should be checked, cleaned thoroughly and dried before using it in other waterways to avoid spreading the species further.  

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