Acting Senior Sergeant Mark Lucas, of Invercargill, said last night the investigation was continuing and no decision had been made yet if the driver would be facing any charges.
The container of household rubbish from the Mataura waste transfer station became unbalanced as it was being transported to a landfill near Browns, about 5pm on Thursday.
It took the truck it was on with it when it toppled off the bridge near Channel Rd on State Highway 96, between Gore and Winton, spilling up to 150 litres of diesel from the truck and 500kg of rubbish into the river.
The 32-year-old driver of the truck was uninjured in the crash.
Environment Southland senior technical officer Graeme McKenzie said there was some initial concern the rubbish could enter the river and contaminate connecting waterways, but an aerial inspection yesterday found little evidence of waste material floating in the river.
Most of the diesel was contained by a boom placed across the river 3km to 4km downstream from the bridge on Thursday night.
The truck and its load were cut free of each other and removed from the river yesterday morning.
The remainder of the estimated five tonnes of rubbish from the container was transferred to another container using a digger and by hand.
The container was hoisted off the river bed, tipping the refuse on a beach beside the water.
The rubbish was then reloaded into a new container by the digger, with Environment Southland staff shifting some of it by hand.
Inevitably, some of the refuse had reached the waterway but there was remarkably little evidence of it in the river and the environmental impact was minimal, Mr McKenzie said.
Staff completed the clean-up yesterday.
It was "quite likely" Environment Southland would seek costs from the owner-operator of the truck for the clean-up operation, but the matter of further penalties had yet to be discussed, he said.
"We were just focused on getting it cleaned up today."
If people found rubbish on the river banks they were asked to either remove it or call Environment Southland on 0800 76 88 45.
