Mr Vivers said these swells, which accumulated energy and travelled at breakneck speed, could create waves of once-in-a-decade sizes across the southern half of WA. A nice wave breaks "unsurfed" off City Beach on Friday morning. Credit:Allen Newton He expected Perth beaches to get waves of up to perhaps eight feet while south-west towns such as Margaret River can expect 20 to 25-foot swells. Swells of up to 50 feet could strike more exposed stretches of coast. Perth's Scarborough Beach was dotted by hundreds of surfers on Friday morning.

He said these swells, though much desired by big wave riders, could be dangerous for inexperienced surfers or swimmers and rock fishers around Perth, Rottnest, Albany and all the way up the coast to Geraldton. They would probably reach Exmouth by Saturday. Surfers and bodyboarders were quick to take advantage of the heightened swell in Perth. Credit:Allen Newton "There will be risk of beach erosion around places like Trigg and Scarborough, even Cottesloe, and places such as Lancelin and Seabird," he said. "It's quite a dangerous situation for inexperienced people around the water, and especially for fishers – don't get in the water if you don't know what you're doing."

A massive storm in the Southern Indian Ocean will set up the largest swell of the year for WA on Friday and the weekend. Credit:Fremantle Sea Rescue/Twitter Surfing WA events manager Justin Majeks said people all over the world had been monitoring the "big blob" over the Indian Ocean for days and preparing their "big wave equipment" – jet-skis, used to reach waves too fast to paddle onto, as well as fins, tow ropes, leg ropes and rescue sleds. He knew surfers in Bali and Victoria preparing for the flow-on effects and thought there was a "very real chance" eastern states and even international surfers were booking flights to WA. While the swell is exciting surfers it threatens more erosion in Seabird Credit:Emma Young He said The Right, near Albany, one of Australia's most notorious surfing spots and the site of Taj Burrows' infamous quest for the greatest surf photo of all time, would be pumping.

Perth surfers, many heading to stand-up paddleboarding and longboarding titles in Mandurah over the weekend, were excited about "the great unknown"; the "phenomenal" wave that could prove their biggest-ever. Lancelin will be under threat of erosion by the swell. Credit:Thomas Cameron "It's created some great hype," he said, but issued words of caution to less experienced surfers. "The experienced guys know what to expect and prepare for but even in Perth it'll be quite big, so go to places you surf at a lot or already know quite well, go with a friend and stick to the wave sizes you're confident with, because it will be pretty crowded as well," he said. Mr Majeks said prospective spectators could head just about anywhere – Cottesloe, Leighton, City, Trigg, Ocean Reef or Two Rocks beaches, to name a few.

"This weekend, you'll be spoiled for choice," he said. The anticipation in the coastal towns of Seabird and Lancelin, however, is closer to nervousness than excitement. Only a month ago, the Shire of Gingin spent $35,000 restoring the beach and infrastructure at Grace Darling Park, Lancelin, washed away by the swells from the last big storm. In the town of Seabird, about 40 kilometres south, 15 private homes as well as public utilities are threatened by beach erosion that has worsened over the past 12 months to the point that the next big swell might be the last for some houses already on the edge of a sharply eroded coastline. An emergency solution of concrete reinforcing mats, a stopgap to a longer-term strategy, is being worked on frantically, but state government permissions to carry out the works are still being finalised.

Shire chief executive Jeremy Edwards said everyone was waiting with fingers crossed that disaster would not strike on the weekend now that safety was within reach. "We are worried ... we are always worried about Seabird and Lancelin," he said. City of Stirling chief executive Stuart Jardine said the council had highly responsive beach services and natural areas teams that monitored the coastline during events such as these. Follow WAtoday on Twitter