The lower level of Dún Laoghaire east pier will be closed from today as work begins on a major refurbishment programme.
The project will see the resurfacing of both the east and west piers over the next three years at a cost of €15 million.
It is the biggest repair job to be carried out on the piers since the harbour was built in the early 19th century.
Phase one, starting today, involves the east lower - the section most used by the public - and is expected to take 26 weeks.
It will include work on the wharf, which was added to the pier in 1827 to accommodate the Admiralty Mail Packet, and on Berth No 1, built for ferries in the middle of the 20th century.
The new surface will be laid out in bays using a mixture of concrete and seashell, with the boundaries between bays marked by strips of Irish granite.
A number of public parking spaces near the National Yacht Club will be unavailable to the public while the €3 million first phase is under way.
The Dún Laoghaire Harbour Company, which is funding the work from its commercial activities, said it had raised with Dún Laoghaire/Rathdown County Council the poor state of the east pier's bandstand and shelter. Both come under the council's responsibility.
The company also hopes to announce plans soon for a major extension to the harbour's 450-berth marina, a key factor in its increased profits last year.
Meanwhile, the development proposed for the old mailboat terminal at Carlisle Pier is expected to be the subject of a planning application to the council early next year. The scheme includes a national marine-life centre, a 127-bedroom hotel, 229 apartments, and retail and leisure uses.