Hannah Miley was one of five British swimmers to secure Olympic places with her victory in the 400m medley at the national trials in London.
Miley was joined by Aimee Willmott, Robbie Renwick (400m free), Roberto Pavoni and Joe Roebuck (400m medley) in making the British team for the Games.
To guarantee a place, swimmers need to finish in the top two in their event and also make the 'A' standard time.
The GB Paralympic trials are also taking place at the Aquatic Centre.
It is the first time the venue has been used for a competitive swimming meeting, with the capacity this summer set to be 17,000 before it is reduced to 2,500 post-Games.
Speaking on day one of the test event, London 2012 chairman Lord Sebastian Coe said he considers the swimming centre "to be the gateway to the (Olympic) Park - 75% of people coming into the Park will be through this gateway - and we thought it was really important we made this the iconic venue".
The likes of double Olympic champion Rebecca Adlington and 50m backstroke world champion Liam Tancock must see off challengers from across the nation over the next week if they are to make it to the Games.
One of Britain's leading medal hopes will definitely be there after Scotland's World Championship runner-up, Miley, swam an impressive four minutes 32.67 seconds in the 400m medley, while Aimee Willmott joined her in making the Olympic team with an English record of 4:37.48.
"I wasn't really expecting that time," said Miley. "I am really chuffed with how it went, it felt great. The crowd and the atmosphere was electric so it is going to be really exciting how it is going to be at the Olympic Games.
"It's taken a huge pressure off me knowing I've made it, I've done what I needed to do. I can hopefully enjoy the rest of the competition."
Keri-Anne Payne, who will look to add to her open water world title at the Olympics, is keen to make the pool team but was fifth in the 400m medley and will now look to qualify in the 800m freestyle.
Pavoni earlier became the first British swimmer to guarantee their place in the Olympic pool in August by winning the 400m medley in 4:12.43, with Roebuck also getting the required time in second place.
"It's unbelievable," said Pavoni. "I'm 20 years old, it's my first Olympics, I've been dreaming about this ever since we found out in 2005 it was going to be here.
"I live just 20 minutes down the road - I might even stay at home for the Games. It's one stop on the train from my home town to Stratford so you can't get much closer."
Renwick dominated the 400m freestyle with a winning time of 3:46.73, but Dave Carry was an agonising 0.23 seconds outside the 'A' time in second.
Adlington will go in the 400m freestyle on Sunday, while Fran Halsall, Jemma Lowe and Ellen Gandy will battle it out in the 100m butterfly and Tancock will begin his 100m backstroke campaign.
The situation for Paralympic hopefuls sees three places available on Team GB, with a second national trials to come in Sheffield from 6-8 April. Only after that will the three fastest swimmers in each event make the team.
World record holder and multi-Paralympic champion Ellie Simmonds, 17, won the MC 400 free in 5:27.09 ahead of Hannah Russell, who set an S12 British record of 4:46.76.
"It's amazing to know the public were all watching and it's great that they've stayed on to cheer us on, because everything helps," Simmonds told BBC Sport.
Jonathan Fox (S7) won the MC 400 Free, Jessica-Jane Applegate the MC 200 Free, and Stockport's Dan Pepper took the MC 200m free in 2:02.73, ahead of Ben Procter and Craig Rodgie, with all three under the qualification time.
"I'm very pleased with that," Pepper told BBC Sport. "I would have liked to go a bit faster but getting the qualifying time is excllent, so I'm happy with that at this time of the season."