Freckles the horse looked up helplessly after falling into a muddy ditch.
But there was a happy ending to her ordeal.
She was spotted in time by a passer-by, who plunged into the icy brook and held her head above water until a team of firefighters came to her rescue.
The 20-year-old Highland-cross was in danger of drowning in the water-filled dyke after she became stuck.
Freckles' owner thinks the greedy mare may have tried to munch on the rich grass near the dyke, lost her footing and tumbled in.
Fellow horse owner Karen Saunders was in a field with other horses when she saw Freckles plunge into the water in a field near Lancing College Farm, in Coombes Road, Lancing, on Monday evening.
Karen ran to the scene and phoned for help from other riders who use stables nearby.
Jackie Taylor and her husband Lee were out walking their dog while their daughter Emma, 12, took a ride on her horse, who shares a field with Freckles.
Jackie, 42, from Sompting, was asked to help.
She said: "We turned round and went straight to the dyke. Freckles was getting panicky."
She and Lee, 46, jumped into the water to help hold Freckles' head above water. The horse had become so exhausted trying to climb up the mud bank she had given up and rolled on her side. Jackie said: "She was breathing funny and she kept shaking. Then she started shutting her eyes."
Freckles' owner, Caren Whyte, was alerted and abandoned work in a nearby bar to be with the pet she had owned for 13 years.
Mother-of-two Caren, 27, was hysterical when she saw Freckles in the water. She said: "I thought she was going to die. I just jumped in.
There was no way she could have held her head up herself."
Freckles suffers from arthritis and is considered a veteran because of her age. Three years ago she was accidentally kicked by another horse and suffered a broken hock, which needed £5,000 of treatment. Since then her mobility has been reduced and she was unable to climb out.
Caren said: "She was shaking in the water and her eyes were shutting like she was giving up. The rescuers shouted at her to keep her awake."
The group held on to the horse's head for half an hour until the fire service arrived. Three crews arrived just after 6.30pm and, after failing to encourage Freckles out, launched a manual rescue.
Dave McMahon, station officer at Shoreham, was at the scene with his crews and specialist animal rescue-trained firefighters from Storrington.
Mr McMahon said: "The water was only about waist-deep for us but it's quite a hazardous job.
"A horse can give a kick or a bite but a kick can be dangerous. It was also slippery, which made it hazardous.
"We use a strop which goes around the horse's legs and we pull it out.
"It sounds quite barbaric in a way but the crews from Storrington are really experienced. They did a fantastic job."
Using manpower the horse was pulled from the ditch and on to her feet before being greeted by her tearful owner.
Caren, from north Lancing, stepped away while more than six people pulled Freckles by her legs.
The animal was pulled out and got to her feet almost immediately. Caren said: "She was shivering. I stayed with her until 11.30pm."
Caren returned yesterday morning and said: "She was whinnying at me. I can't believe how perky she is. I thought it was done and dusted when I saw her in the water.
"She loves me to death. I've had her for 13 years and we've been through everything together."
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