Walczak got off to a flying start as she led the final after 300m, however she slipped down to fourth by the midway stage.
She needed to dig deep to bring home a medal, doing exactly that as Walczak finished in 7:54.12 minutes to take bronze.
"I tried to treat this like every other race and not let the occasion get to me", said Walczak.
"So when I was coming into the medal raft I had to remind myself that this was the Senior Worlds and I'd got a medal. It was a brilliant feeling.
"It's been fourth, fourth, fourth all season and it is so good to get a medal finally."
Walczak's bronze had been proceeded by the lightweight men's pair final in which Aldred and Scrimegour also claimed the final podium step.
Italy led early with the Swiss not far behind and Great Britain in fourth before moving back up in into third place in time for the final attack.
"I think we had a pretty good row and just ended up getting tired at the last bit", said Aldred.
And they could be plenty more for Great Britain to celebrate as another three boats qualified for finals in the Olympic classes.
Frances Houghton and Vicky Meyer-Laker were dominant in their double scull semi-final to win in 7:13.45.
"It's the first time that I've made a World Championships final in a small boat so I'm really pleased", said Houghton.
Great Britain's other semi-final win came from the lightweight men's four of Chris Bartley, Will Fletcher, Jonno Clegg and Adam Freeman-Pask. They paced their race to perfection to slide past a tiring New Zealand in the final 200m.
Single sculler Alan Campbell put in a measured semi performance that saw him take second behind London Olympic silver medallist Ondrej Synek.
However Vicky Thornley just missed out on the women's equivalent in fourth while Matthew Langridge and Bill Lucas finished in the same position in the men’s double scull.
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