Ferry giant Stena Line has started a consultation on its plans to bolster Holyhead breakwater in a bid to stop it falling into the sea.
The historic breakwater was built between 1848 and 1873 using rock from the nearby Holyhead mountain.
But over the decades rock in front of the vertical wall has been steadily lowering as waves slowly grind down the rock into smaller pieces and wash them off the mound.
There are now concerns that this will leave the vertical wall at risk of collapse in the coming years.
This would allow large waves into the harbour and make the port untenable for users - including ferry services run by Stena and Irish Ferries.
Stena, who are working with Dutch engineering consultants Royal Haskoning, said: "To prevent the collapse of the structure, Stena Line have planned the construction of a long-term, robust refurbishment.
"Many options have been considered, and the conclusion of this assessment was that rock or concrete armour is required to bolster the existing mound."
They said sufficiently large armour rock required to provide protection against the large storm waves is not available from the international market and they have chosen to go with two layers of concrete armour units.
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The tetrapods would be placed in a double layer along the breakwater at the foot of the seaside wall over a width of approximately 40m.
They added: "In the long term, the visual prominence of the concrete armour would be reduced due to the effects of weathering, algal growth and general patination.
"Storm and exceptional sea conditions will cause a limited amount of displacement to some of the tetrapods which will provide minor visual relief to the otherwise highly regimented, linear arrangement of the units."
They concluded: "The proposed scheme would provide a permanent solution to the constant erosion of the foundations of the breakwater and damage of the blockwork-walled super-structure; thereby ensuring the continual protection of Holyhead Town and the port, as well as preventing the potential loss of the breakwater and lighthouse themselves."
A consultation into the proposals
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