Vanuatu's geology, mine and water department says the crater lake of Manaro on Ambae has turned red and scientists were sent to the crater at the weekend to study its activity.
Manaro erupted last year for the first time in 121 years, forcing thousands to be evacuated.
A geohazards manager at the Vanuatu geology, mine and water resources department, Esline Garae, says they are not sure why the lake changed its color.
"Because it could be just a chemical reason, so we can not say anything about this yet. But it is true that the color has changed."
Ms Garae says the volcanic eruption on Lopevi remains graded as level 2 volcanic activity, but heavy ashfall has eased.
Another volcano eruption rated at level 2 is Yasur on Tanna.