The scarf is hoped to be ready by 18 May 2011
A group of knitters are busy creating a scarf long enough to wrap around Porthmadog's famous Cob.
The embankment, built to reclaim land from the Glaslyn estuary by developer William Maddocks in 1811, will reach its bicentenary next year.
There will be a fireworks display, concert and triathlon to celebrate this feat of engineering.
But local knitters fancied marking the occasion with a spot of yarn bombing, also known as graffiti knitting.
"It all started in America," said Delyth Owen, who helps run three knitting groups in Porthmadog, Caernarfon and Llangefni.
"They find lamp posts or fences and cover them in something they've knitted, to cheer a place up.
"So we decided to knit a scarf for the Cob. Someone's said it's 1,700 metres long, another told me it was 2,500, so we'll go for something in between."
The Cob is a 1.4km long sea wall between Porthmadog and Penrhyndeudraeth
It was built to seal off the Glaslyn estuary from Tremadog bay as a land reclamation measure
Maddocks made the investment when it was thought the London to Ireland route would include a ferry terminal at Porthdinllaen
His finances were saved in the 1830s when the Cob became a vital part of the railway from the Ffestiniog slate quarries to Porthmadog port
The A487 road was added later on the landward side of the Cob
Some of the women are being sponsored for each metre they knit, with proceeds going to Alder Hey Children's Hospital, Liverpool, and the North Wales Air Ambulance.
Delyth is confident there'll be enough knitters to help as the hobby has regained popularity of late but other people can get involved, knitting a scarf 6-8 inches wide and a metre long in any colour or wool.
"Schools are also finding out that it's one of those things that help children's concentration, hand-eye coordination and counting skills," said Delyth, who's aiming to have the scarf ready by 18 May.
This will coincide with a walk across the Cob by local school children, some from the Penrhyndeudraeth end and some from Porthmadog.
Two halves of the scarf will be brought along with them and sewn together in the middle.
More details available from Siop Anna, Porthmadog, or call 01766 515011.