Six-year-old Jessie was yelping for help but her owners were unable to get down to her and onlookers were urging them to stay safely on dry land.
Luckily, Littlehampton RNLI came to the rescue after being called out by the coastguard on Sunday morning.
Ray Pye, volunteer lifeboat press officer, said: “The owners were able to coax Jessie out of the water onto a small shoal bank at the mouth of the river.
“The lifeboat and crew arrived at the scene at 9.01am where they were able to get Jessie safely on board. The lifeboat returned to the station slipway, where Jessie was reunited, unharmed, to her very grateful owners.”
Ray of Hope, Littlehampton’s D class inshore lifeboat, was launched by the volunteer crew at 8.54am on Sunday in response to a call from the UK Coastguard.
Mr Pye added: “The call reported that there was a dog in the water at the entrance to the harbour.
“Jessie’s owners had just completed an eight-mile run with her alongside, when they reached the side of the pier wall.
“Jessie continued onwards and jumped over the wall and ended up in the river. The owners, trying to respond to her yelps, were unable to get down to her.
“The tide was coming in and members of the public on the opposite side of the river were urging them not to go into the water.”