The Transportation Department had to close one side of the Glenfinnan Bridge after workers found some of the wooden piles were rotten.
Darrell Evans, the department's design and bridge maintenance manager, said the bridge has timber piles that helped hold it up, but staff noticed a problem when they saw a dip in the road Friday.
"Three of the five (pilings) on one side were completely rotten so we had to close one side of the bridge down," he said.
The bridge on Fort Augustus Road is down to one lane and the department imposed weight restrictions as a precaution.
Evans said there were no noticeable problems with the bridge's roadbed earlier in the week, but when staff went by Friday they saw a significant dip in the road.
If staff hadn't noticed, there could have been serious problems from vehicles crossing it, he said.
"It could have been quite catastrophic, depending on the weight of the vehicle."
In 2008 the province implemented a bridge inspection system to make sure P.E.I.'s 1,335 bridges were safe.
When auditor general Colin Younker looked at the bridge inspection program for his 2009-2010 audit, he found several problems, including some bridges that weren't inspected every year.
After the audit's release, then transportation minister Ron MacKinley said the province had caught up on its inspection cycle.
Evans said the Glenfinnan bridge is inspected once every two years as part of the provincial bridge inspection program and it was checked last year.
The department also had it on the list for replacement next year, he said.
"It was scheduled to be replaced anyway."
Evans said department staff will review the situation next week and look at how best to proceed, including whether to fix or replace the bridge and how much all the options will cost.
"We don't have a game plan in place yet, but we'll work on that," he said.