Heavy fuel leaked from a power station in Manipur's Imphal valley and spilled into streams flowing alongside it, officials said on January 11.
The incident happened on January 10 at night at the Leimakhong power station in Kangpokpi district. Streams passing through villages such as Kanto Sabal and Sekmai were affected by the spill, they said.
These streams meet the Imphal river -- the lifeline of the region -- downstream, they added.
The Chief Minister's Office (CMO) directed the departments concerned to take "immediate necessary action to prevent an environment calamity, making use of all available resources in terms of machinery, manpower and expertise".
Heavy machinery was deployed to divert the flow of the water in the affected streams towards fields, an official told PTI.
"It is yet to be determined if miscreants were involved in this or if it was accidental," he said.
Locals said the water of the streams is used by them for daily chores.
"Not just aquatic life but also the communities that depend on the water have been severely threatened by this spill," said Nongmai, a resident of Kanto Sabal.