Mr Smith said inquiries into what had occurred revealed the driver of the car had been racing a ute.
"It appears the utility failed to negotiate a corner and crashed through a fence," he said.
The car managed to take the corner but crashed into a bank, bounced over another and crashed into the river.
Both drivers were breathalysed, with the driver of the car returning a result of 486mcg and the 22-year-old driver of the utility returning a result of over 600mcg, police say.
The legal limit is 400 mcg.
The passengers in the car and a passenger in the utility were all unhurt in the crashes.
Mr Smith said the car in the river remained submerged two to three metres below the surface.
"Police are still assessing what, if any, further charges may result from this morning's incident," he said.
"In the end, poor decision making, speed and alcohol all appear to have been contributing factors in what so easily could have ended up as a tragedy."