Employees working on a river flow experiment at the Aerospace and Mechanical Engineering building, 1130 N. Mountain Ave., dumped approximately 300 gallons of green-colored water on East Helen Street Friday afternoon, causing police to block off traffic for 30 minutes.

Traffic to the area was suspended until a HazMat crew was able to confirm that the liquid was non-toxic.

Tucson Fire Department was also called in until the issue was resolved.

Gary Hopkins, an instrument maker close to the project said nothing dangerous was dumped into the street, although the color was suspicious to those outside the building.

"It just happened to be the perfect color of anti-freeze," he said. "It's a glowing, visual thing."

The experiment was contained in a large water container that charts the movements of river currents. The dye used in the experiment is also used in oceanic water-rescues, he said.

"We know there's nothing wrong with the stuff," he said.

Once the HazMat crew confirmed that the liquid was not dangerous, the police and fire departments left the scene.