Part of Lake Taupō was turned bright reddish-orange after a truck crashed, spilling its load of krill oil and milk powder.
Police said the crash occurred around 4.30 on Sunday morning on SH1, Motutere, between Waitapu and Te Heuheu.
The road was closed until about 10.45am Monday.
The Waikato Regional Council (WRC) explained the situation on Facebook and said it had consulted experts about how to remedy it.
“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 WRC wrote.