Crews are working to move a truck - believed to be full of sewage - which rolled over on Morshead Drive outside the Royal Military College at Duntroon on Thursday morning.
No one was injured in the crash, which occurred at 10.52am.
Police said the truck was carrying sewage and according to an emergency officer on the scene, about 20 thousand litres had to be emptied before it was able to be cleared.
Lanes were closed near the Morshead Drive and Staff Cadet Avenue roundabout.
Police also closed the exit ramp from the Monaro Highway around 1pm and diverted traffic via Fairbairn Ave.
Crews were still working to lift up the truck as of 12.55pm.