Biologists are continuing to monitor watercourses around an oil refinery near Immingham after an explosion and an oil spillage.
The spill happened when an overland pipeline fractured
Two workers were injured in an explosion at the Lindsey Oil Refinery in South Killingholme on Tuesday.
Investigations are also being carried out to find out how crude oil seeped into the Humber from the refinery which is threatening wildlife sites.
An Environment Agency spokesman said it appears the oil is now dispersing.
The cause of the leak is thought to be a fractured overland pipeline.
The oil had spilled into the South Killingholme Drain, an effluent drainage channel which feeds into the South Killingholme Haven area of the estuary.
There had been fears that the leak could impact heavily on the wildlife habitat.
The South Killingholme Haven is surrounded by mudflats which are used as feeding and breeding grounds by many species of birds and other animals, including water voles.
The spokesman said: "We do not expect any long-term impact on water quality. However, we will continue to monitor the situation.
Threat to wildlife
"An investigation has been launched into the source and the cause of the incident."
Officials from the RSPB, English Nature and North Lincolnshire Council are at the site assessing the threat to wildlife.
Ten oiled redshank birds have been found by volunteers helping in the cleaning up.
An RSPB spokesman said: "Although we're very concerned about reports of oiled birds, we are optimistic that the worst has been averted because this spill was spotted relatively quickly.
"But we are very concerned that there was a large element of luck involved and we would want any inquiry to focus on how these pollution incidents are dealt with in future."
The Environment Agency said its investigation could take several weeks to complete and would seek to determine whether legal action could be taken and how to prevent any future spills.