Du Toit, who has already proved herself as a serious open water prospect in her home country of South Africa, takes a step towards achieving her goal of Olympic qualification by competing on the international circuit.
The South African will face Britain's World Championship silver medallist Cassie Patten as well as top Australian athlete Trudee Hutchinson who is currently ranked top three in the FINA series.
In the men's competition, Egyptian Mohamed Zanaty is one of the favourites having finished top two for the last two years in London while Britain's Alan Bircher, who won the London leg last year, will be hoping to see a return to form after a slow start to the open water season.
The FINA event is one of two international competitions taking place at the London Regatta Centre in the Royal Albert Docks this weekend, with the LEN (European) Open Water Swimming Cup Leg (5km) also part of the two-day programme (Saturday 16 June).
Bircher and Patten open the weekend of competition in the LEN 5km, and are joined by fellow Brits Kerri-Ann Payne, Simon Panting, Richard Charlesworth, Rachel Jack and Alice McCall.
For Patten and Payne, the Festival of Open Water Swimming is the third event in an intensive nine-day period of competition that has seen the duo compete at the LEN event in Spain as well as the Barcelona Mare Nostrum.
Patten, who won the LEN 10km event last year in London, is looking forward to competing on home soil.
"I've only been competing in open water for just over a year so I'm using every swim to gain experience before Beijing," she said. "There are people competing in the sport with years of experience so it's difficult to predict how I'll do.
"We'll be competing against a lot of the swimmers from Seville and even Barcelona as quite a few teams are doing the same route as us, but they're not looking forward to the cold water in London.
"I'm used to swimming in cooler temperatures so I'm really looking forward to coming back to England and it also means my family are able to come and support me."
Competitors from more than 20 countries are taking part in the Festival of Open Water Swimming, including teams from Russia, Mexico, Argentina and Croatia.
The British 10km and 5km champions will be determined from the World and European event while Britain's young swimmers will be tested over a shorter 3km distance in the 3km Junior International.
Highlights from Sunday's FINA event will be broadcast on Sky (schedule to follow).