CHICAGO - Investigators and prosecutors are finally getting to the bottom of the nasty episode involving alleged illegal lavatory dumping by the driver for a tour coach operated by the Dave Matthews Band.

Nearly six months after the incident, the driver has been charged with dumping 800 pounds of waste onto a sightseeing boat that was cruising the Chicago River last summer.

Stefan Wohl was charged with misdemeanor counts of reckless conduct and discharging contaminates to cause water pollution. The charges carry a maximum penalty of one year in jail and a $10,000 fine.

Wohl, 42, of Selma, Texas, turned himself in to Chicago police last month and was released on his own recognizance.

Authorities say Wohl was driving alone to a downtown hotel Aug. 8 when he emptied the bus lavatory tank as it crossed the metal grates of a bridge.

The waste poured through the grates and onto the open deck of the Chicago Little Lady tour boat, which was passing below with more than 100 people on board.

Prosecutors used surveillance tapes and consulted with engineers about the dumping before filing charges. "We were satisfied with what they told us that it could not have been an accident," said prosecutor Robert Egan.

No one was physically hurt in the incident but many boat passengers, like Nancy Todor, said the waste made her "physically ill" and "extremely nauseous." She is suing the band.

The Chicago Architectural Foundation, which operates the boat tour, said they received many angry calls from passengers demanding compensation for clothing and personal items.

Illinois Attorney General Lisa Madigan has filed a lawsuit seeking $70,000 in damages against the band and driver Wohl, alleging they violated state environmental laws.

At the time, a band spokesman said Wohl had said he was not involved with the incident. The driver reportedly has cooperated with investigators, although he has not admitted to the dumping.

The investigation has been especially lengthy in part because the bus was traveling with the band and had to be returned to Chicago to be examined.

In October, the band posted a notice on its Web site saying that although "we still do not have a definitive understanding of what happened," the band would work with affected passengers to "make things right for all concerned" and make $50,000 donations to both the Chicago Park District and Friends of the Chicago River.

The band's statement said the incident "is awful and it goes against so many principles we hold dear: environmentalism, accountability and, mostly, principles of humanity."

Prosecutors said the band has cooperated in the investigation, including flying violinist Boyd Tinsley, who used the bus, from California to Chicago to be interviewed, and bringing the bus back to the Chicago area for inspection