Firefighters rescued a horse stuck on its side in thick mud, spotted by a member of the public.
The RSPCA were also called to the field in Old Swan Lane, Hailsham at 8.30am yesterday, where 12 horses are being kept.
It is understood the horses are living on private land without the permission of the owner, known as 'fly-grazing'.
An East Sussex Fire and Rescue spokesman said the horse, about 12 hands high, was stuck lying down in the mud when crews arrived.
He added: “Animal Rescue Unit crews put strops underneath the horse and lifted the animal, onto firmer ground.
“Crews then used warm water spray to help warm the horse up and remove mud from the animal.
“A vet was also in attendance and the horse was given steroids and warmed up further.
“Once the horse was ready, it was hoisted upright into a standing position, with support from the strops.”
A spokeswoman for the RSPCA said it was a “complex situation” and notices have been issued to the owners suggesting the horses are moved to a better location.
She added: “The horse is very cold and tired but otherwise appears to be in good health.
“We arranged for a vet to attend and transport her to their premises so she can be cared for while we try to locate her owner.
“The RSPCA has been working with World Horse Welfare to help the horses on this field. The horses appear to be in fair to good body condition, have access to natural shelter, grazing and water.
“Conditions at the field are not ideal but the horses' basic needs are being met so legally there is very little more we can do.
“We understand that there are current legal proceedings taking place and hope these result in the horses being moved to a more suitable location.
“We really appreciate members of the public keeping a close eye on these horses and would like to reassure them that we are doing all we can to help them.”
British Veterinary Association president and vet Robin Hargreaves said: “The terrible flooding has devastated many areas and it will be a huge relief for residents to see the waters subside.
“Unfortunately, the challenges for animal owners remain, as contaminated water continues to pose a threat to pets and livestock.”