The EA initially visited the site on Sunday and installed absorbent material to stop the oil from spreading.
The agency expects most of the work to be completed by Friday, but staff will continue daily monitoring visits to assess any lasting environmental impact.
Phil Chilvers, who reported the spillage, said: “It’s been down to the community to get things going, which is a shame as when it was reported [in December] it should have been done. But it’s great [the clean-up] is happening now.”
Lee Barron, the Labour MP for Corby and East Northamptonshire, said he would visit the site on Friday.
“We’re liaising with local residents, the local angling club, and the parish council… to make sure we can support the residents and then make sure we have something in place to ensure that this never happens again,” Barron added.
Thornely said the agency receives thousands of pollution reports each year, but described this one as “a very significant incident”.