Divers of the Colombian army retrieved on Sunday the first of 100 cyanide cans that fell into the country's principal Magdalena River in a ferry accident early Saturday.
The recovered can was "unbroken", which Environment Minister Juan Lozano said was "good news".
"It is in good state. This allows us to think that the rest will be taken out very soon," he said.
At least seven trucks sank in the river in the accident that took place near the city of Gamarra in the northeastern province of El Cesar. As there were cyanide and other fuels on one of the sunk trucks, all the river's aqueducts were ordered to be closed.
A group of 14 divers are now working to bring afloat the rest of the cans. Lozano said he would visit the zone soon together with Colombian President Alvaro Uribe.
Rio Magdalena Corporation, the company that was in charge of the transportation of the trucks, said "the ferry's obsolesces or a nightly back current" were the possible causes of the accident.
Luz Amanda Pulido, director of the Attention and Disasters Prevention Bureau, alerted the riverine municipalities in El Cesarand nearby provinces for the consequences of a probable contamination.