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.
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