Commonwealth Games officials are to investigate whether the quality of the water in the practice pool is causing illness among the swimmers.
England's team leader John Atkinson said 20% of the swim team, including Rebecca Adlington and Fran Halsall, have suffered with stomach problems.
Australia are blaming the practice pool for several of their team being ill.
"It's a matter we'll deal with with the greatest of urgency," said Commonwealth Games Federation chief Mike Fennell.
"We must find this out immediately. If there's something unsafe you can't swim in that water.
"We have ensured the water quality is tested, and food. We don't have specific reports about illness and the reasons why.
I don't think I'm very well to be honest
English swimmer Fran Halsall
"We are concerned if athletes are not well and cannot perform at their best. We haven't had specific reports of swimming being different from the rest."
Fennell was also questioned about reports of condoms blocking toilets in the athletes' village.
He replied: "If that is happening, it shows there is use of condoms and I think that's a very positive story, that athletes are being responsible."
England duo Halsall and Adlington both admitted they were feeling unwell on Wednesday.
Halsall, one of the favourites for 100m freestyle gold, looked out of sorts, although she still managed to win a bronze medal.
The Liverpudlian cut short a post-race interview with BBC Sport's Sharron Davis to stop herself from being sick.
She said: "I don't think I'm very well to be honest. I came down with a bit of a tummy bug and had nothing to give, I pretty much couldn't stand up after my final. I need to go before I am sick on you."
Team Doctor Ian Gordon added: "Unfortunately she is just one of quite a few who have gone down with this but she is a bit more high-profile than some of the others.
"It is hygiene related. They have been assiduous in their personal hygiene but everybody is going down with this acutely."
Adlington, who is due to swim in the 800m freestyle final later on Thursday, won a relay bronze on Wednesday before saying on her Twitter feed: "Got a bronze on the 4x200 tonight! Girls did amazing! Very proud! Hoping I feel better tomorrow though, not flash at the min!"
A Commonwealth Games England statement read: "As of today there are 541 England team members in the Village. Over the past 28 days 8% of our team have had some kind of mild stomach conditions.
"These levels are lower than we expected coming into this environment. But we are not complacent and continue to reinforce the need to be vigilant in areas like hand hygiene.
"Separately, we have asked for reassurances as to the water quality at the aquatics venue."
Fennell and Games organising committee chairman Suresh Kalmadi were also asked about ticket sales and if over zealous security was putting spectators off attending.
"Ticket sales are going up and most of the major issues have been sorted out," claimed Kalmadi. "Ticketing is not an issue any more."
Fennell also apologised for an incident at the athletes' village in which three Ugandan officials, including the team's chef de mission, were injured in their vehicle at an entry gate.
A 'tyre killer' device was activated after the radio frequency reader failed to read the vehicle's sticker.
The sharp-edged barrier which stays below the ground when authorised vehicles pass over it rose suddenly and hit the vehicle, leading to the occupants suffering minor cuts and bruises.
"We regret the incident at the athletes' village very much," said Fennell.