The City of Cape Town says a bright green liquid which a resident recently spotted running into the ocean in Sea Point is a coolant used for commercial building cooling systems.
"The City has identified various companies that both manufacture and use this substance in the servicing of commercial cooling systems but, as this investigation is ongoing, the City cannot release further detail at this stage," said transport and urban development mayoral committee member Brett Herron.
He said the companies had a responsibility to correctly dispose of excess or used coolant when servicing cooling systems.
The toxic coolants also come in shades of blue or pink.
"The City will be engaging with the various companies with the intention of making them aware of their responsibilities and the fact that it is illegal to discharge this substance in to the City's stormwater system," said Herron.
The City said it would distribute the relevant information to residents and businesses in Sea Point, Green Point and Camps Bay.
This information included how dumping pollutants into the stormwater system affected coastal water quality, where and how to discharge products safely, and how to report sightings of illegal substance discharges.
Atlantic Seaboard councillor Shayne Ramsay said she was doing her bit to alert locals of the consequences of putting these substances into the water.
"Lots of people don't know what a stormwater drain is or where the water ends up," she said.
Meanwhile, warning signs would remain up at Clifton First Beach for a few days after a sewage spill earlier this week.
Safety and security mayoral committee member JP Smith said on Wednesday that the spill emanated from a sewer blockage at a nearby property and they were hoping to repair that as soon as the team was able to gain access.
"Any form of full-contact recreational activity, such as swimming, diving, water skiing, surfing, paddle skiing and wind surfing may increase the risk of gastrointestinal problems, as well as skin, eye, ear and respiratory irritations."