AN investigation has been launched after swans were found caked in deadly diesel fuel on the River Colne.

The Environment Agency said an officer was on standby this weekend in case the situation worsened.

The alert came after at least three swans covered in the sticky fuel were rescued by volunteers on Friday.

They warned countless more creatures could die if the oil cannot be cleared.

It is not known if the diesel was dumped deliberately.

An Environment Agency spokesman said it was unable to trace the source.

It is believed to have got into the river on the freshwater side of the weir and then flowed into the tidal side.

Staff at Wildlives rescue centre in Thorrington treated three mute swans which were captured by the RSPCA.

Centre boss Rosie Catford feared the adult birds – two males and one female – are just the tip of the iceberg.

She said: “They are caked in diesel. It doesn’t look as bad as black oil, but the stench is awful. It gets everywhere and you can taste it all the time.

“We’ve got three so far, but there is another we have been trying to catch for ages and it looks like there will be more.

“If you can imagine trying to get oil out of the feathers of something the size of a swan – it’s a hard job.

“They have very thick, downy feathers held together a bit like velcro which makes them waterproof and insulated.

“When they get diesel on them, they try to preen it off and ingest it, which causes serious internal problems so we’ve got to address that as well.”

Diesel oil breaks down the feather structure, making them less waterproof. The repeated washing process makes it even worse.

Rosie said: “They get very distressed and we get very distressed trying to clean them in hot soapy water and then hosing them down for ages.

“Once we have a clean swan, they have to preen that velcro back into place again. If we just let them go, they will soak up water like a sponge and drown or get hypothermic.

“If they are not all treated and washed they are going to die a slow and painful death.”

Oil-covered swans have been see in the Colne at Riverside, East Hill and the Hythe, in Colchester.

RSPCA officers have been using special swan hooks to rescue the birds before taking them to Wildlives to be cleaned up.