World Rowing Championships 2010
Venue: Lake Karapiro, Waikato, New Zealand Dates: 31 October - 7 November Coverage:
Live action & highlights on BBC TV, Red Button and online (UK only)
Purchase & Hunter strike gold for GB
Zac Purchase and Mark Hunter added a world title to their 2008 Olympic gold in the lightweight men's double scull.
Britain's Frances Houghton and Debbie Flood also returned from a year off to regain their crown in the women's quad.
But Great Britain's defending world champion men's coxless four were dramatically dumped off the podium after leading for much of their final.
Last year's bronze medallists in the women's lightweight double finished fifth, as did the GB men's quad scull.
The conditions were brutal as a strong side-wind on Lake Karapiro appeared to favour the near-side lanes.
Especially in the last 600m, that was not a fair course
GB Rowing performance director David Tanner
"The golds were fantastic," said GB Rowing performance director David Tanner.
"Not everyone would have predicted the women's quad. The lightweight men's double really showed their mettle in the semi but they both really stepped up to the mark in really hard conditions.
"I'm gutted for the men's four, it's a big loss, and disappointed also for the lightweight women's double. There's no question it was unfair. You have to deal with choppy, cross-wind conditions, and there's no question some people did that better than others.
"But on the near side it's no coincidence that a very large number of crews came through who had been well beaten in the earlier rounds. Especially in the last 600m, that was not a fair course."
Mike Tanner, chairman of governing body Fisa's events commission, said in a statement: "Based on (the fairness committee's) observations, they considered that the conditions did not justify taking further steps under the provisions of the Rules of Racing."
GB women blow rivals out of the water
Purchase and Hunter put in a commanding display to beat Italy by a boat length in the lightweight men's double scull, while defending world champions New Zealand were third.
Purchase, from Gloucestershire, missed last season because of illness while Londoner Hunter took 12 months off to coach in California and has suffered illness and injury this season.
But they showed no signs of their early-season form struggles, dominating after taking a half-length lead from the off.
"It feels awesome," said Hunter. It's something I've been searching for and training for for a long time. To be Olympic champion and not a world champion, there was a little hole there, but that's been filled now.
"We've had a lot of challenges along the way but we've overcome them. It's probably made us better as a combination than we were when we won gold in Beijing.
"We wanted to move on and show that we could and we've done that. There's only another 20 months to London so it's going to get exciting."
Houghton and Flood also took a year off after the disappointment of being pushed into the silver-medal spot by China in Beijing in 2008, when Katherine Grainger was in their crew.
It just felt like a scramble. There's no way it was fair. It's a bitter pill to swallow
Flood, who spent the time qualifying to become a prison officer, returned to form and fitness in a single scull this season but Houghton has been injured and managed to win a fourth world title in her first big event since Beijing.
Their delight in victory was emphasised by Annabel Vernon, the fourth crew member in Beijing, who stood up in the stroke seat in an emotional celebration after powerfully overhauling world champions Ukraine in the second half of the race.
Gloucester's Beth Rodford was the only remaining member of the quad that finished fifth in the world final last year.
Houghton said: "It's pretty incredible. I don't think it's sunk in at all. It was such tricky conditions. We had that opportunity and we said, 'let's just take it by the horns and just go for it'. It was a brilliant race.
"It definitely ranks right up there. I would never have expected this, neither when I first came back nor this morning. It just feels amazing."
The men's four - Britain's only winners in Poland a year ago and a favourite to repeat here - could not match that dominance, though, leading by as much as a length for three-quarters of the race.
After suffering a "crab" - catching a wave around the 750m mark - Alex Partridge, Richard Egington, Alex Gregory and Matthew Langridge gradually conceded their lead to France in the outside lane.
They looked powerless to hold on as Greece stormed past in the last 500m and, roared on by the home crowd, New Zealand also pipped them to the line.
France win as GB faves fade
"It's pretty difficult to explain," said Langridge. "We're bitterly disappointed. Without making excuses, it was so difficult out there. It didn't feel like racing.
"We got a good start but the conditions just seemed to swing more and more round to a cross wind and, being the far side of the course, we seemed to get the worst of it.
"Every time we tried to make a move, it just seemed to get worse and worse and we were spending our whole time steering. It just felt like a scramble. There's no way it was fair. It's a bitter pill to swallow."
Men's pair Andy Hodge and Pete Reed face a battle to overhaul New Zealand's reigning champions Eric Murray and Hamish Bond at the 12th attempt on Saturday.
But, unless they do so, coach Jurgen Grobler is likely to add the duo to a re-jigged four next season, aiming to have a better chance of Olympic gold in 2012.
Great Britain's women's lightweight double scull, Hester Goodsell and Sophie Hosking, also struggled with the rough water on Friday, having been fastest qualifiers for their final.
Canada's Lindsay Jennerich and Tracy Cameron took and early lead and survived a challenge from Germany while the reigning champions from Greece snatched third.
Britain had qualified for the final of the men's quadruple sculls for the first time since 1982, when Steve Redgrave was in the crew.
But Olympic bronze medallist Stephen Rowbotham and talented youngsters Charles Cousins, Sam Townsend and Bill Lucas were never in the hunt as Croatia pipped Italy to the line for the country's first world title in an Olympic event.
The British crews all wore black ribbons in memory of double Olympic champion Andy Holmes, Redgrave's former pairs partner, who died recently, at the age of 51.
The second of three days of finals in New Zealand starts at 0135 GMT on Saturday.
Single sculler Alan Campbell takes on friend and arch-rival Mahe Drysdale, who pushed him into second place last year and is eyeing a fifth successive world title, but Czech Ondrej Synek is the form sculler of this season.
"My job is to get a medal," said Campbell. "There are four of us that can definitely contest that but the order will really come down to a little bit of luck on the day.
"Hopefully the luck will be on my side and I'll come out on top."
GB's lightweight men's four, containing 2007 world champions Richard Chambers and Paul Mattick, plus Rob Williams and Chris Bartley, look set for a tight battle for medals.
And women's pair Helen Glover and Heather Stanning also have a chance of a place on the podium.