One worker has been fired, now several others face disciplinary action after they were caught on camera dumping materials into the Hillsborough River.
Now, city leaders are working to make sure it doesn't happen again.
"I just couldn't believe it," Matthew Von Dohre told ABC Action News.
So appalled, he went back the next day to the Riverwalk hoping to see something different.
Again, he was disappointed.
"I knew it was illegal," said Von Dohre, who is studying to be an architect and work in the construction field.
"I wanted it to stop."
So, Von Dohre took out his camera and recorded a video that has already gotten one person fired and has Tampa's city leaders demanding answers.
Von Dohre shot video of a construction team dumping concrete wash into the Hillsborough River as they worked on Tampa's signature project, the Riverwalk.
"This was an incredibly stupid thing for them to do," said Ali Glisson, a spokesperson with the mayor's office.
Glisson said the Mayor's Office has demanded a written statement from the Johnson Bros. Construction Company. It asks what happened, why it happened, and what the company planned to do about it.
Glisson also said a member of the Hillsborough County Environmental Protection Commission is now monitoring the construction team at all times.
"It's been a big priority for us to get (the Riverwalk) built and this is not the way it's supposed to be done," Glisson told ABC Action News.
Johnson Bros. tested the water once the mistake was identified. They told the city that the water in the Hillsborough River is still within normal limits, with turbidity levels reading once at 2.53 NTU and 3.62 NTU (nephelometric turbidity units). The threshold is 29 nephelometric turbidity units.