The Kangaroo Island Council and boat owners that use the slipway at the Kingscote jetty have vowed to fight to save the structure.
The Department of Planning, Transport and Infrastructure on May 30 wrote to slipway users informing them of the pending closure of the only facility on KI where boats can be hoisted out of the water for repairs and maintenance.
Blaming "on-going low usage", DPTI has advised boat owners to use facilities at Wirrina Cove and Port Adelaide instead.
Eco-tour charter boat skipper Andrew Neighbour brought his jet boat out for its annual hull cleaning last Wednesday.
Closing the slipway would not only inconvenience the KI's commercial and recreational boating community, it was also a safety issue.
A commercial crayfishing vessel that began taking on the water on the South Coast two years ago was just one vessel saved by slipway.
"I've had to put a sinking vessel up on it, heaps of vessels have been spared sinking because of the slip, heaps," Mr Neighbour said. "It's not a huge fix and as I said a new trolly will give us five-plus years, we just need incorporate a catchment of sorts to meet EPA standards."
Slipway operator Anton Jamieson and Mr Neighbour said the problem was that successive governments had failed to do maintenance.
The KI Council discussed the issue at its meeting this week. Mayor Michael Pengilly said he was quite upset about the closure.
The council will write to the Minister expressing concern and asking for the closure to be deferred pending further discussion.
American River marine radio operator Carol Miell, who this week received an OAM for services to marine rescue, said slipway was vital for marine safety in the area.
Backstairs Passage was one of the most treacherous stretches of water in the world and asking damaged vessels to cross it could potentially be disastrous, she said.
Regarding its proposed closure, she said, "I am dead against it."