Authorities are still trying to determine the source of a weekend fuel leak into the Missisquoi River in Swanton.
The Swanton Fire Department successfully contained an oily sheen on the Missisquoi Saturday afternoon.
Officials with the Vermont Department of Environmental Conservation said that the sheen seemed to be bubbling up from under a sluice wall, which has water channels that lead into the river.
Beyond that, local and state officials haven't been able to figure out where it's coming from.
Swanton police chief Leonard Stell said Saturday that the leak seems to be made up of heating oil or diesel fuel.
Since the origin of the fuel is unknown, authorities haven't been able to figure out how much has spilled.
Stell credited the Swanton Fire Department's fast response with preventing much of the contamination from spreading downstream.
Officials said the sheen on the surface was mostly gone Monday morning.