They say it was caused by a leak in a pipeline that runs from New Haven to a facility in East Haven.
Officials say the fuel that spilled is number two fuel oil. They say they lost approximately 2,000 gallons, but they have recovered about 1,800 gallons from the river. According to the officials, they have containment booms in place.
According to investigators, crews are working to seal the faulty pipe. Crews will continue to work in the area for the next few weeks to make repairs to prevent this from happening again.
Experts say there is no sign that wildlife has been impacted. The Connecticut Department of Energy and Environmental Protection does not believe this poses any threat to the environment beyond the area of containment.