insidethegames understands that an idea to use the course at Gifu that hosted the 2005 World Championships has been rejected on technical grounds and because, at 400 kilometres from Tokyo, the site would isolate rowers completely from the rest of the Games.

Instead, rowing courses in the Tokyo area are being assessed for suitability, with World Rowing anxious to ensure that the eventual venue is close enough to enable rowers to stay in the Olympic Village.

"This is not guaranteed at the moment," Jean-Christophe Rolland, President of World Rowing, told insidethegames.

He added: "It is not an easy situation."

A plan to move the Olympic rowing venue to Gifu, which hosted the 2005 World Championships but is 400 kilometres away from Tokyo, has been abandoned ©Getty Images

It is still possible, even in the more parsimonious era ushered in by Agenda 2020, that the venue outlined in the Tokyo 2020 candidature file - the so-called Sea Forest Waterway - will get the go-ahead.

This new facility, to be created from an existing water channel bisecting an island in Tokyo Bay, was costed in the candidature file at around $78 million (£50 million/€64 million), plus $23 million (£15 million/€19 million) for Games-time overlay.

It was stipulated as the venue for canoe sprint events, as well as for rowing, and would remain as a new sports and leisure facility after the Games.

This price-tag does not appear too steep even in today's comparatively straitened times for event planners.

The problem has arisen, or so Insidethegames has been told, chiefly because of additional costs, notably for a factory demolition, that while not necessary from a competition standpoint would be highly desirable to achieve the best possible legacy for the city.

"If Tokyo wants to invest in that area, that is fine, I will support it," Rolland said.

"But I don't want to be seen as the sport that has cost all that money when much of the expenditure is not related to the sport."

Rolland went on: "I cannot say if we will be at Sea Forest or not."

With little more than five-and-a-half years of preparation time remaining, the clock is ticking, and it is hoped that a solution will be settled on in weeks rather than months - particularly as this seems to be part of a much broader rethink with up to 14 sports possibly affected.

The Sea Forest area alone is supposed to host venues for three others sports, besides rowing and canoeing.

The candidacy file foresaw the construction of temporary equestrian cross-country and mountain bike courses on land to either side of the Sea Forest Waterway.

Uncertainty surrounds the future of Wakasu Olympic Marina, which was supposed to be a permanent facility that would provide a legacy after Tokyo 2020 ©Tokyo 2020

Meanwhile, a new permanent sailing marina - the $105 million (£68 million/€86 million) Wakasu Olympic Marina - was planned for the other side of Tokyo Gate Bridge.

It is hard to say whether there would be a knock-on effect for these nearby venues if Sea Forest Waterway were dropped as an Olympic facility.

Tokyo 2020 said this month that it had been reviewing the original venue plan since June, with the review conducted from the perspectives of "legacy, the impact of the Games on Tokyo residents and venue construction and maintenance costs".

It emphasised that Agenda 2020 seeks to promote "maximum use of existing sporting facilities for a reason of sustainability", adding: "We believe that the broad direction of our reviewing work is in line with the philosophy of the Agenda."

John Coates, the International Olympic Committee (IOC) vice-president who chairs the IOC's Tokyo 2020 Coordination Commission, last month underlined the IOC's wish for the Games to make maximum use of existing facilities, saying he thought this overrode the "eight kilometre philosophy" that underpinned the original bid.