TOKYO — High levels of bacteria forced the swimming portion of a triathlon test event for the Tokyo Paralympics to be canceled on Saturday.

It’s the second setback in the triathlon for organizers of next year’s Olympics and Paralympics. An Olympic triathlon running event was shortened from 10 kilometers to 5 kilometers on Thursday because of what the International Triathlon Union called “extreme levels” of heat.

Tokyo’s hot and humid summers are a major worry for Olympic organizers. The water issues are a reminder of the Rio de Janeiro Olympics three years ago when high bacteria and virus levels were found in waters for sailing, rowing and open-water swimming.

In a statement, the ITU said E-coli levels were “more than two times over the ITU limits.” It said the water was at Level 4, the highest risk level.

E-coli bacteria, which normally live in the intestines of animals and people, can produce intestinal pain, diarrhea and a fever.

The venue in Tokyo Bay, called Odaiba, has been a concern for organizers, who have experimented with different measures to clean the water in the area, located in an urban part of central Tokyo.

The ITU is scheduled to hold it final test event on Sunday “depending on the latest water quality tests”, it said in a statement.

A few days ago the ITU described water quality conditions at the venue as “very good.” However, swimmers at a recent distance swimming event at the same venue complained of foul-smelling water.

The water temperature at the venue on Saturday was 29C (84F), with the air temperature hovering above 32C (90F).

Tokyo spokesman Masa Takaya said, “we are set to conduct a comprehensive review with the international federation.”

He said a triple-layer underwater screen will be installed for next year’s Olympics, replacing a single-layer.

“Based on the results of multiple research in the past, we believe that the multiple layer screen will assure the successful delivery of the competitions,” he said.

Filthy water plagued the Rio de Janeiro Olympics. The South American city lacks a functioning sanitation system for much of its population. Open water there tested high for bacteria and viruses, which confronted athletes in rowing, sailing and triathlon.