Chicago officials chose to shut down an Earth Day demonstration they say was unsafe. The organization GreenPeace put six wind turbines on the Michigan Avenue bridge downtown. Nicole Granacki is the spokesperson for the group.

GRANACKI: The city came and did ask us to remove the wind turbines. So our staff and volunteers did bring them down.

Granacki acknowledges her organization did not have a city permit to put up the wind turbines. Brian Steele is a spokesperson for the Chicago Department of Transportation.

STEELE: The installation this morning was something none of us were aware of and we don't allow anything to be afixed to bridges. Particular our moveable bridges. The installation that was put in place this morning is definitely a potential safety hazard.

Steele says the Michigan Avenue bridge is very sensitive to weight and must be balanced.