Officers aboard the Dallas Police Department's helicopter spotted an unnaturally bright red liquid Saturday draining into White Rock Creek in South Dallas.
Now, it is being investigated as a case of possible illegal dumping.
"It's important for companies and individuals to know that nothing can go into a storm drain or the waters of the state except rainwater. Detergents, motor oil, or any kind of hazardous waste is forbidden by law," said Interim City Marshal Paul Hansen.
The city called in a remediation company to pump out the liquid and dig up the nearby dirt to contain the spill. Samples have gone to a lab for testing.
The material isn't believed to be hazardous, and investigators believe it may be detergent used in car washes.
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"If this material, let's say it is a detergent, makes it into the Trinity River System, you could have major fish kills," Hansen said. "You're affecting people's drinking water downstream, so it's just important that the water remains as clean as possible."
Hansen believed the liquid was contained as of Monday afternoon and there was no immediate threat to drinking water.
A man at the scene who works for a company at the site on Beall Street in Dallas was detained, but not arrested. Hansen said investigators will determine what charges the man may face once water and soil tests are complete.
An employee who answered the phone at the company said they don't work with hazardous materials. The man told NBC 5 the company's owner was out of town and couldn't comment on the investigation.