Rio de Janeiro will not make good on its Olympic pledge of slashing the flow of raw sewage and garbage into the Guanabara Bay, where the 2016 Games’ sailing and windsurfing competitions are to be held, the state’s top environmental official has acknowledged.

The promise to cut the flow of pollutants into the bay by 80% was a key part of the city’s Olympic bid document and widely held up as among the most enduring legacies of the games. But with just one and a half years to go before the showcase event, it has become increasingly clear that the target wouldn’t be met.

Rio’s new state environment secretary, Andre Correa, told reporters on Friday he couldn’t provide an estimate of how much officials would actually succeed in cutting the flow of pollutants into the bay.

“Removing 80% of the pollutants? It’s not going to happen, it’s not going to happen,” said Correa, who took office earlier this month.

Still, he insisted that regardless of how far the cleanup progresses, the Olympic events will not be compromised.

“From the point of view of the Olympics, the point of view of water quality, what I’ve said about the 80% does not at all affect the courses” for the sailing events, Correa said. “There’s no big risk for sailors having troubles with illnesses and such things.”

“I’m not worried about the water quality in those areas, I’m much more worried about floating garbage there,” he said, adding that the so-called “eco-barriers”, nets that are strung along the mouth of rivers and meant to filter out garbage before it enters the bay, “aren’t working well at all”.

“I’m going to change that,” he promised.

Sailors’ associations have expressed reservations about water quality as well as the garbage, both of which they say could harm sailors’ health. Olympic sailors have described the 2016 venue as a “sewer”, complaining of the stench at the events’ main venue, the Gloria Marina, and describing having to dodge floating sofas, animal carcasses, and plastic trash bags that foul rudders in the open waters. A few sailors have said they got sick after falling into the bay.

Correa said he was not sure whether Olympic authorities have been informed that the cleanup pledge will not be met.

With most of the sewage in the greater Rio area flowing untreated into area rivers, its showcase beaches and the bay, Correa estimated a $3.8bn investment would be needed to bring sewerage to the entire metropolitan area. With no timetable for the release of such sums, it is unclear when that might happen, he said.

The bay cleanup has been a sore spot in Rio’s fitful Olympic preparations almost since the city won the Games back in 2009. Environmentalists have consistently warned that even with the clock ticking, nearly nothing has been done.

Last year, the Associated Press obtained a letter to then sports minister Aldo Rebelo, in which Rio’s state’s former environment secretary acknowledged in a best-case scenario that pollution flowing into the bay could be cut to “over 50%” – well below the promised reduction of 80%. Rio’s mayor, Eduardo Paes, later said he was “sorry that we did not use the Games to get Guanabara Bay completely clean”.

Rio’s pledges to clean up the bay stretch back decades, with generous funding consistently reaping little in the way of concrete advances. While the decline of industry in Rio helped cut down on the levels of heavy metals in the bay, the galloping spread of informal, unplanned “favela” slums and other settlements has helped turn much of the once-crystalline bay into a virtual open sewer. An overpowering stench emanates from much of the bay, and beaches are off-limits for swimmers. Tons of household trash line the bay’s coastline and form islands of refuse.