Dark colors in aerial photos of a creek flowing into the Trinity River are pig blood from the Columbia Meat Packing Plant according to Dallas County Health Director Zach Thompson.
"It no longer appears to be blood, it is blood," Thompson said.
Authorities executed a search warrant at the plant on 11th Street Thursday searching for evidence about the source of the blood and who is to blame.
"Any waste should be discharged into proper containers, properly disbursed to a city facility, that deals with wastewater," said Thompson.
He said investigators visiting the plant found pipes that bypass proper waste disposal.
"The search warrant will determine how long it has been going on. From what we can see from how it looks, it has been going on a while," Thompson said.
A resident taking aerial pictures of the Trinity River with a miniature plane first reported the discovery to authorities in December.
Google Earth pictures recorded in March 2011 also show the dark flow into the river from Cedar Creek behind the plant.
Dallas City Councilman Dwaine Caraway who lives nearby said neighbors have complained about the sound of pigs and the foul odors from the plant.
"There’s been a stench as you cross the MLK Cedar Crest Bridge for more than 50 years," Caraway said.
The councilman is angry but not entirely surprised to learn about accusations of improper waste handling.
He welcomes the investigation.
"The citizens of this city are first and this is a no-brainer that something is wrong there," Caraway said.
Several agencies are responsible for enforcing environmental laws at the plant.
Representatives from several of them said they could not comment about past dealings with the plant because of the pending investigation.
NBCDFW could not immediately locate prior inspection reports.
Former Dallas US Attorney Richard Roper said the company and its officials could face serious penalties if willful violations of the law can be proven.
"The penalties could range from an administrative civil penalty all the way up to serving time in state or federal prison. It can be that severe," Roper said.
An operator answer the telephone at Columbia Meat Packing said the company has no comment.
An attorney for the company did not return a telephone message Friday.