A detailed inspection has found a series of failures that will need to be fixed before allowing pedestrian access.
Alderney's long breakwater is highly exposed to storms and the power and impact of Storm Goretti has punished it further.
A detailed inspection has revealed holes along the lower section.
The upper section, which has the railway tracks, is undermined in places and debris can fall onto those walking below.
This makes the structure unsafe for leisure walkers or anglers, as the breakwater is a popular place to fish.
The slipway at the beginning of the structure, below Fort Grosnez, is sheltered and so is unaffected by storms.
Guernsey's Environment Committee, whose political members recently had a tour of the breakwater, say the gate stopping pedestrian access also means fisherman can't land their catch.
This will be replaced to allow slipway access while also shutting off the long mole until it is made safe.
Haut Du Mont: Jury fails to reach verdict on third gas worker
Schools in Guernsey to close for Storm Austen
States of Guernsey 'carefully monitoring' forecasts for Storm Austen
Haut du Mont: Gas workers convicted of manslaughter
Guernsey government websites go offline amid security concerns
Guernsey mum creates autism awareness books inspired by son
Crisis meeting over the standard of Guernsey's bus service
Storm preparedness advice for Guernsey air passengers and boat owners
