The mural of a child holding a spade with Tesco sandcastles in the foreground was painted by the artist on the back of steps leading down to a beach in St Leonards in 2010, and is a big draw for tourists visiting the Hastings area.
The council put up a perspex screen to protect the piece after it was vandalised, but the wood and rusty screws holding the screen have come free from the steps in places, exposing the artwork to the elements.
A 1cm-wide gap on the top baton allows rain to fall directly on to the famous work.
A similar-sized gap on the right upright lets in sea spray from the waves.
The screen is defaced in places with green paint, and the bottom part of the Banksy is obscured by the longshore drift of pebbles.
The mural has faded over the years - which is in the nature and spirit of street art - but is noticeably more deteriorated where the screen has come free from the wall.
Residents say the council should take urgent action to preserve the piece for future generations - pointing out how the Banksy is a prized work and draws in tourism.
Sarah Scott, 41, from Lewis Road, Hollington, fears that unless it is protected soon, “it will be lost forever”.
“We’ve got to protect it. We don’t want it getting trashed,” she said. “It needs protecting from the salt water and stuff. It’s very open to the elements. The wood’s already started to degrade. It can’t be that difficult - I mean they’ve already put a frame up, so just reinforce it and put some waterproofing round it.”
She added: “There should be signs up as well showing where it is, because you’re never going to see it from up there (on the promenade). A sign saying ‘we have our own original Banksy’.”
Debbie Cutting, 55, who runs a daily ‘beach boogie’ class near Azur Marina Pavilion, about 100 yards from the Banksy mural, said: “It needs to be protected because if you see how the sea elements deteriorate a building with the wind and the rain and the salt alone, it definitely needs saving. They could easily spend some money to save it. And it’s not an expensive job, let’s face it. It attracts tourists as well - some Banksy fans travel a long way to see it.”
Jamie Edwards, 30, from St Leonards, added: “It’s a two-minute job, it would hardly cost anything. Hastings council has already just received a huge grant - and they’re opening a restaurant in the town centre, which they’re spending millions on where the public toilets were, so they’ve definitely got funds.”
However, Tina Morris, who runs Coastal Currents, a group supporting local artists and musicians, believes Hastings Borough Council has done all it can to protect the Banksy.
“They covered it in perspex at their own cost and considering street art is outside in the public realm and usually open to the elements, the artist is aware of that process of erosion as part of the art,” she said.
“The council do their best to upkeep murals like the Coastal Currents West Hill mural by ATM of the Black Redstarts as they know how much the public love and want to keep it.”
Tina said it is not possible for the council to restore the Banksy piece, and added: “The best course of action - if we love and value the work so much, and if we feel it is a crucial part of our cultural offer - we need to acknowledge the importance of finding a budget to pay professional street artists and commissioning them to keep this town current and relevant on the street art scene. As the more this town is on the map for high quality street art, the more likely Banksy is to return and give us the gift of a new piece.”
Hastings Borough Council has been contacted for comment.