The wave-shaped venue is the last permanent building to be completed in London's Olympic Park, a former industrial wasteland that has been transformed in one of Britain's biggest-ever building projects.

Rogge watched local swimmers test London's first Olympic-length pool, while a women's synchronized swimming team performed to the strains of Queen's "We Will Rock You" in the 269-million pound ($442-million) facility.

"I have seen so many venues in my life that I had a visual shock when I came in," Rogge said. "I came in from the top _ everything stands out; the harmony, the quality, the innovation. It's a masterpiece." The International Olympic Committee president was in London to formally invite the world's athletes to the games at a ceremony on Wednesday night in Trafalgar Square.

"I am very optimistic for the remaining year to come and I think we will have a great games," Rogge said.

In central London, British Prime Minister David Cameron marked the milestone by inspecting preparations for a beach volleyball test event at Horse Guards Parade next to his Downing Street home.

Later in the evening celebrations, 17-year-old Tom Daley will take the first dive at Olympic Park three days after qualifying for his second games.

"Only a few years ago, this was a distant dream," the 2009 world champion said. "The fact that I qualified at the weekend and am taking the first dive is a complete privilege. I can't wait for next year and the honor of representing Team GB." The 17,500-capacity aquatics center, which will also be used for swimming, synchronized swimming and water polo events, had been expected to be among the first major projects to be finished and one of the boldest architectural statements on the 226-hectare (560-acre) east London site.

Instead, it was completed after the 80,000-seat Olympic Stadium, the velodrome, handball arena, basketball arena and the International Broadcast Center.

The aquatics center design was scaled back in an effort to cut spiraling costs even before Britain slumped into recession.

While retaining the sweeping, wave-shaped roof, the size of the venue was reduced to prevent it becoming a white elephant after the games have finished. Two giant wings of temporary seating have been added to accommodate fans, but will be dismantled after the Olympic to leave a 2,500-seat venue.

"The extraordinary regeneration in east London, all the opportunities, the nation's and region's engagement _ I can't look at that Olympic Park without taking pride," organizing committee chairman Sebastian Coe said.

London has experienced few of the distractions that overshadowed the one-year countdowns to the previous two Summer Games.

Beijing was battered for its record on Tibet and human rights before the 2008 Olympics, while Athens struggled to the last minute to finish venues in 2004.

Even the worst global recession for more than 70 years failed to significantly derail London's plans, with test events already under way and the IOC relaxed about the final 12 months before the games returns to London after 64 years.

Security and transportation remain the biggest challenges.

The British government has been planning for the national terror threat to be classified as "severe" during the Olympics, meaning an attempted attack is highly likely. A day after London was awarded the games in 2005, homegrown suicide bombers attacked London's transportation network, killing 52 people.

"Security is permanently under review," Coe said. "We have the right teams in the right place. We will do whatever we have to do to provide a safe and secure games." "The key is finding the right balance," he added. "We do big events pretty well in this country. We want people to feel welcome without the city being locked down." Filling venues has not proved to be a problem. In fact, "a world record-breaking demand for any sporting event on the planet" _ according to Coe _ has provoked anger about the ballot process for tickets.

"Everybody's sort of whipping this up into a bit of a storm but peel the layers back: the problem here is essentially that we had 22 million applications for 6.5 million tickets," Olympics minister Hugh Robertson said.

"One in four people are going to be disappointed and there's nothing we can do about that. If we'd built stadia of twice the size, we'd have faced huge international criticism for building white elephants that couldn't be used afterwards ... everybody else around the world thinks this has been one of the greatest successes that the Olympic Games has ever seen." In a year, successes will be judged for each nation by medals, which will be revealed for the first time on Wednesday.

Britain's challenge now is ensuring its athletes are not burdened by the growing home expectation to match _ or surpass _ the fourth-place finish in the Beijing medals' table.

A year from now, London will be welcoming 10,500 athletes from more than 200 countries, 5,000 coaches and team officials, 20,000 media personnel and hundreds of thousands of visitors. The 17-day festival will feature athletes competing in 26 sports in more than 300 medal events in 32 venues.