The probe continues into the source of an oily substance that contaminated the Water and Sewerage Authority's Caroni Water Treatment Plant last week.
A release issued today by the Environmental Management Authority (EMA) did not confirm the source of the contamination.
After several tests in the area, the EMA's response team did not find "any visible evidence of contamination" in the riverside vegetation and at the mouths of drains emptying into the Caroni River.
"The EMA however continues its investigations and is urging the public to come forward with any information on suspected illegal dumping of waste which may have led to this event," the release said.
The EMA will be taking "a zero-tolerance approach to both companies and contractors if proper certification and responsible handling of waste chemicals is not carried out," the release said.