The Environment Agency says it is investigating the spillage of a large amount of diesel at a Burton Latimer site.
In November cereal makers Weetabix spilled the fuel and took action to prevent it from entering the River Ise.
It is now working with the Environment Agency to prevent further pollution but further action may need to be taken.
Manfai Tang, environment management team leader with the Environment Agency, said: “The Environment Agency was notified in November by a company in Burton Latimer of the loss of a large quantity of diesel from their site.
“The company took action to contain the spill to prevent the diesel entering the River Ise, and we provided them with advice and informed other river users in the area of the situation in order to minimise the impact on the environment.
“We are continuing to work with the company to ensure no further pollution affects the river, and we have an ongoing investigation to determine whether further action is required.
“We’d urge anyone with concerns or who wants to report suspected pollution to call us straight away on our incident hotline at 03708 506506.”
The exact amount of diesel lost is not known but it is believed to be more than 10,000 litres.
Angler Gary Goodson often fishes in the River Ise.
He says had it not been for the work of the Environment Agency, it could have been a ‘massive disaster’.
He said: “There was a big oil slick but I didn’t see any dead fish.
“It’s not so much of a disaster but it could have been had it not been for the Environment Agency.
“What they’ve done down there is marvellous.
“They [Weetabix] are a massive company and things like that shouldn’t happen.”
A Weetabix spokesman said: “The spill on our land last year was promptly reported and swiftly contained to avoid potential damage to the river.
“We have since worked closely with the Environment Agency to investigate the cause of this problem and prevent its recurrence.
“Our reputation as good neighbours and active members of the community is important to us and we will strive to uphold this.”