Part of Lake Taupō was turned red on Sunday after an overturned truck saw milk powder and krill oil spill into the water.
The crash occurred at Te Pōporo (Bulli Point), south of Taupō.
The Waikato Regional Council says the oil was the reddish-orange tinge seen.
"Experts we’ve been talking to say the oil will likely start to breakdown through a combination of sunlight and wave action, and the water will help to dilute it, too," the council said.
"While we haven't seen any oiled birds, there is a potential for the oil to stick to bird feathers. We don't know what effect this might have, but it's thought the krill oil will break down a lot quicker than mineral oils."
Water samples had been taken for analysis.
"Many of you will know that krill oil is a popular dietary supplement, but our advice is to avoid taking lake water for drinking/household water in the proximity of the crash site."
Hapū Ngāti Te Rangiita issued a rāhui in the area.
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