Nine passengers were taken to area hospitals.
The boat's captain says everything was fine until he applied reverse thrust to slow the vessel down as it approached the dock. Nothing happened. The engine did not respond.
The bow of the brand new $2 million boat is banged up, and so are 20 of the 150 people who were on board.
"We were approaching the wall, I thought, very fast, and then someone yelled, 'Hold on!' and we just hit it!" said passenger Becky Bauer.
Passengers report the 90-minute cruise was perfect up until that final minute when the sightseeing boat hit the concrete dock without warning or slowing.
"Suddenly we hit and all these chairs came flying from behind us and everybody fell on the floor."
"I heard 'Hold on!' and there was nothing to hold onto because it's all folding chairs fell and we just fell forward," said passenger Diane Fleisher.
The impact knocked people over. Some scraped knees and arms. A few had to be carried off the boat. Firefighters say it could have been much worse.
"You also have to remember that when you are coming in are thinking they're coming," said Deputy District Chief Ken Wojtecki of the Chicago Fire Department. "They're standing up. So you probably had some falls and bruises."
The boat, named Lila, is brand new. Wendella put it into service Friday. The captain reports the engine simply quit during docking.
"The boat should slow down effectively with the reverse. It did not. The engine, or something in the engine, made it not work, a malfunction of some type," said Wendella Boat Tours spokesman Thom Serafin.
Monday night, Charlie Chaa, 11, is nursing cuts on his arm and leg. He described his first river cruise as "bad" and indicated that he did not feel inclined to take another.
Passengers are offering praise for the crew, who they say quickly helped everyone off. The boat will be out of service until the Coast Guard can determine what went wrong. Wendella has several other sightseeing boats that will continue to operate.
Wendella Boat Tours spokesman Thom Serafin released the following statement Monday evening:
"This evening Wendella Boat Tours vessel The Lila ran into their dock near the Michigan Avenue bridge on the Chicago River.
"Wendella, a third generation family-owned business that has been working on the Chicago River since 1935, is very concerned with the guests who were on board and extends our well wishes.
"Wendella is conducting a full investigation in conjunction with the United States Coast Guard, who has jurisdiction over the Chicago River, but preliminary information suggest engine failure as the probable cause of the incident."