Environment Agency and Fire service trying to find source.
Teams are working to trace the source of fuel pollution - believed to be diesel - at Coney Gut on the Taw Estuary.
The Environment Agency says the incident is contained and the environmental impact is minimal. No fish or wildlife harmed, it added.
North Devon Council has warned boat owners in the area that they may have residue on their vessel.
The @EnvAgencySW are on the case with the fuel spill at Coney Gut in the Taw Estuary. Boat owners - please be aware that if your boat is moored in this area it may end up with residue left on it #NDevon https://t.co/O7IuQEACJl— North Devon Council (@ndevoncouncil) 25 June 2019