Dead fish float on the edge of Guanabara Bay, part of which will be the sailing  venue for the Rio Olympic Games (Mario Tama / Getty Images)

In the latest problem for the sailing venue for the 2016 Olympic Games in Rio de Janeiro, thousands of dead twaite shad have been found floating in the waters of Guanabara Bay, prompting an investigation by the city’s environmental agency.

Massive die-offs of fish are not uncommon in Brazil, according to O Globo, and it is believed that this may have been triggered by a drought. However, the waters have drawn other unwanted attention because they’re polluted by garbage and untreated sewage from the more than 8 million residents of the 15 cities that share the bay’s shoreline. Twaite shad are a small, silverish fish much like herring.

The waters have made headlines because of the presence of a “super bacteria”, sparking concerns about the health risks to athletes.

The discovery of the fish die-off came during a visit Monday by International Olympic Committee, which said the city was making progress in preparing for the games. But only last month the Brazilian government admitted that it would fall short of its goal of reducing pollution at the venue by the August 2016 start of the games. State governor Luiz Fernando Pezao admitted that cleaning up the area has not been easy. “Every time we have a negotiation,” state governor Luiz Fernando Pezao told reporters (via Sky News) on Wednesday, “the bidding process [for the project] slows and postpones things.”

However, Christophe Dubi, the IOC’s executive director of the Olympic Games, remains optimistic that the goal of reducing pollution by 80 percent remains.

“We are still aiming for this goal. We cannot judge until the finish line,” he said. “We are like athletes in that we are pushing toward the finish line and we should respect that every effort is being made.”

A lagoon system in western Rio, beside the sites of the Olympic park, is stressed, too, the Associated Press reports.

The Jacarepagua lagoon system is also filled with sewage and trash, and aerial photos taken Tuesday by the environmental group Olho Verde showed a massive bacterial bloom inside the lagoon that has spilled out onto the Atlantic and a popular nearby beach. Cyanobacteria are single-celled organisms that give the water a vibrant blue-green hue and can sometimes prove toxic to humans and other plant and animal species.

Athletes visiting Rio in recent months for test sailing events complained about health risks and the hazards of encountering floating debris in the waters where they’ll compete.

Rio’s environmental agency noted in a statement that the there was a die-off of twaite shad in the bay last November and that analysis then revealed “neither abnormalities in the water, nor the presence of chemical or toxic substances. Therefore, specialists concluded that the incidents could be related to the intense drought.”