
Thames Water is to be questioned on its decision to pump about 600,000 tons of raw sewage into the River Thames during August's torrential rain.
The company will attend a meeting of the London Assembly's Health and Public Services Committee on Tuesday.
The Health Protection Agency and the London Port Authority are carrying out a study to see if the pollution is affecting people.
Hundreds of thousands of fish have been also been killed.
Joanne McCartney, chair of the Health and Public Services Committee, said: "Only recently, we heard that the Thames was cleaner than it had been for decades - now we are confronted with a sewage slick.
"It is astonishing that one storm could lead to this. The decision to pump such large amounts of sewage into the river has serious implications for both the health of the river and of Londoners.
"The committee will be asking some serious questions about Thames Water's actions and what we can do to try to prevent a reoccurrence."
Last October, the London Assembly warned that the city's Victorian sewage system could not cope with large amounts of rainwater falling during a short period.
In its report, 'London's Water Supply', the committee revealed that the system relied on releasing untreated sewage into the Thames when the drainage system was overwhelmed with floodwater.
This story first appeared on the BBC News site.