Australian head coach Alan Thompson is searching for answers regarding the apparent pollution that has settled over the Olympic pool.
The national team graced the Water Cube for the first time yesterday evening only to find the smog that has blanketed Beijing infiltrating the space-age aquatic centre.
About half of the Australian swim team have respiratory problems and the thin blanket of pollution is a concern with the swimming program starting on Saturday.
Australian Olympic bosses have invested heavily in finding ways to allow the athletes to perform to their potential in the heavily-polluted city.
''I am trying to find an answer to that question ... I did notice the haze,'' Thompson said yesterday.
It had been thought the indoor nature of the pool would safeguard the swimmers from problems such as asthma which is known to afflict world record holders Grant Hackett, Libby Trickett and Jess Schipper.
Not all of the Dolphins attended yesterday's session with stars Eamon Sullivan and Leisel Jones attending the Olympic venue last night.
Thompson said some swimmers had trained at a nearby university pool where there was more space than the packed Water Cube.
The pool deck provided the clearest indication the Olympics are just around the corner as superstars took to the water.
Dutchman Pieter van den Hoogenband, who is trying to become the first man to claim three straight 100m freestyle titles, looked in great shape before his battle over two laps with Australian sprinter Eamon Sullivan.
Korean world champion Park Tae Hwan was also at the Water Cube, plotting his campaign to take down Grant Hackett again in the 400m.
Meanwhile American superstar Michael Phelps touched down in Beijing yesterday but managed to escape a large media throng.
Thompson said it was important for his swimmers to get comfortable in the 17,000-seat environment before the swimming program.
The unique venue has been sold out for months and the setting is expected to be one of the highlights of the Games.
There were no tears on the pool deck this time following Libby Trickett's emotional outburst on first sighting the Athens Olympic pool.
''Everyone will come in and get a feel for the place,'' Thompson said.
Thompson said four Australian swimmers had been drug tested and expected most of the team to be tested before competition starts.
They may have been quiet at the airport but the American swimming team made sure their presence was instantly felt at the pool.
They formed a huddle and loudly chanted ''U-S-A'' before breaking up into their training. Thompson said defending two-time Olympic 100m freestyle champion van den Hoogenband loomed as a major threat to Eamon Sullivan after showing his hand by withdrawing from the 200m freestyle.
Reports out of the Netherlands yesterday said flying Dutchman van den Hoogenband had pulled out of the four-lap race, which he won at the Sydney 2000 Games, to focus on claiming a third successive title in the two-lap dash, a feat only ever achieved by legend Dawn Fraser.
Van den Hoogenband has drifted from the international spotlight after failing to medal over 100m at last year's world championships and then lost his mantle as the world's fastest man when Frenchman Alain Bernard broke his world record.
Sullivan has also dipped under van den Hoogenband's world mark this year and he is expected to fight out the 100m title with the French star and the Italian world champion Felippo Magnini.
But Thompson warns that van den Hoogenband could still be the danger man at this Olympics.
''I don't think you can ever discount the people you know that can win,'' said Thompson.
''Certainly van den Hoogenband and Magnini are people who can win. ''But at the same token if you go into a race looking at people you might be looking at the wrong one.There was no talk at all about Magnini at that meet in Rome and I think you can forget about people like them but it would be a big mistake. AAP