Women's pair Olivia Whitlam and Louisa Reeve became the 12th British crew to qualify for the Olympics, at the last possible opportunity.
The duo finished second to France in the qualifying race in Poznan, Poland, after overtaking Russia late on.
"They rowed out of their skins. They were superb," said GB performance director David Tanner.
However the men's quad finished third in the final, missing qualification by just over a second.
Rowing boat classes explained
"They had a really good go at it - we always knew that it was going to be tough for them to qualify," Tanner added.
The men's quad and women's single - in which Tina Stiller missed out on a place in the final in Poznan - are the only two events where Britain will not feature.
Eleven other boats qualified for Beijing through their performances at the World Championships in Munich last year.
Many of those crews will be in action in the third and final World Cup regatta of the season in Poznan this weekend.
Final line-ups for each crew for Beijing will be confirmed on 26 June.
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