The International Swimming Federation (FINA) has confirmed the Olympic marathon swim qualifier for Tokyo 2020 will be held on May 29 and 30 in Fukuoka.
Competition is set to take place at the Seaside Momochi Beach Park.
The governing body said the men’s and women’s races will be staged in a defined COVID-safe bubble.
A strict protocol will be in place to ensure the safety of athletes and people involved in the organisation of the event amid the coronavirus pandemic.
Fifteen swimmers will secure their places at the Games in both the men’s and women’s races.
Originally nine athletes had been due to qualify through the event, with a further five advancing through continental qualifiers.
All places will now be awarded at the Olympic qualifier in Fukuoka.
One spot will also be on offer to the best Japanese swimmer.
The 15 qualifiers will complete the field for the Games, with both Olympic races featuring 25 men and 25 women.
The top 10 swimmers from the 2019 FINA World Championships in Gwangju have already secured their places at Tokyo 2020.
The women's 10 kilometres marathon swim event is scheduled for August 4.
The men's race is due to follow a day later.
Marathon swimming events were initially scheduled to begin at 7am local time at the Odaiba Marine Park.
Tokyo 2020 announced in November that the events will now begin at 6.30am.
The expectation is that the races will conclude by 9.10am.
The start times were brought forward amid heat concerns.