Yoshi will be released back into the ocean as early as next week or as soon as the summer months have warmed the water around Cape Point.
She will be fitted with a satellite tag as researchers hope to track her journey for up to three years.
Yoshi will also have an entourage of 25 juvenile loggerheads who will be released back into the wild with her.
Two Oceans Aquarium curator Maryke Musson said considering Yoshi was within the sexual maturity range and exhibited certain new behaviours, the curatorial team decided it was time for her to be released.
Yoshi was confiscated from a boat in Table Bay Harbour by local authorities in 1996, after getting caught in a trawler’s fishing nets.
When she arrived at the aquarium she was the size of a dinner plate, with the aquarium team estimating that she was 3 to 5 years old at the time, making her 24 to 26 now.
At a farewell event on Monday, Musson thanked volunteers and staff who looked after Yoshi.
“She got to spend 20 years here with us, she’s an absolute legend, has touched the hearts of many and often drove us insane in between.
“We are proud we played a role in Yoshi’s life to get her to this age. Yoshi is an ocean traveller, and she is going to spend the rest of her years travelling the oceans, and I’m sure having lots of fun.”
The odds of a loggerhead hatchling surviving to maturity are about one or two in 1 000.
Like all sea turtle species, loggerheads are endangered animals.
Threats to hatchling survival include predation by other animals, entanglement in fishing gear; poaching and illegal trade in turtle eggs, meat and shells; coastal development and habitat loss; rising sea temperatures and ocean pollution.
Their average weight is 135kg but they can range from 80kg to 200kg.
Talitha Noble, Two Oceans Aquarium conservation co-ordinator, said: “Yoshi has been one of our longest guests at the aquarium. Aside from her, every year we have a lot of more short-term guests.
“The turtle hatchlings that we get are little loggerhead hatchlings, and loggerheads largely nest on our eastern coastline, northern KZN and Mozambican border, and they come to us because they float down the coastline in the current and when they find themselves in the southern waters here, the water is often a little bit too cold for them, and they get very weak and dehydrated and they wash up on our beaches.”