The lawsuit accuses the band and one of its bus drivers of violating state water pollution and public nuisance laws. It seeks $70,000 in civil penalties.
"Our driver has stated that he was not involved in this incident," band spokesman John Vlautin said in a statement. He said the band "will continue to be cooperative in this investigation."
According to the lawsuit, on Aug. 8 a bus leased by the band was heading to a downtown hotel where members were staying. As the bus crossed the Kinzie Street bridge, the driver allegedly emptied the contents of the septic tank through the bridge's metal grating into the river below.
More than 100 people on an architecture tour were showered with foul-smelling waste. The attorney general's office said no one was seriously injured.
"This incident may be unique, but that does not lessen the environmental or public health risks posed by the release of at least 800 pounds of liquid human waste into a busy waterway and onto a crowded tour boat," Attorney General Lisa Madigan said in a statement.
After the incident, the boat's captain turned the vessel around and took passengers back to the dock. Everyone received refunds, and the boat was cleaned with disinfectant.
The South African vocalist/guitarist formed his band in the early 1990s, and combines the sound of the Grateful Dead with the world-music explorations of Paul Simon and Sting. It also shows the influences of Santana.
The Dave Matthews Band amassed a sizeable following by touring constantly in the 1990s, particularly at college campuses. The music remained fresh with each performance because of fresh improvisations which also make the band more interesting in live performance than in studio recordings.
In 1995, the Dave Matthews Band had the hit single, "What Would You Say." Its 1996 album "Crash" entered the charts at number two and quickly went platinum. Its latest release is "The Gorge" DVD of 2002 performances in Washington state.