A dam in southwestern Nova Scotia releases cascading water from Vaughn Lake into the Tusket River system. More than 200 millimetres of rain fell in four days on the area. (CBC)

Water levels were beginning to recede Tuesday in parts of southwestern Nova Scotia after the worst flooding in a century, emergency management officials said.

But even as levels started to fall, communities hit the hardest were still contending with powerful waters after more than 200 millimetres of rain fell over four days.

On Tuesday at approximately 8 p.m. AT, emergency crews were called to the Tusket Bridge, which had collapsed in the community for which it is named.

"My wife and I were sitting in our front room and all of a sudden we started hearing a rumbling noise," said Gordon Wood, who lives a stone's throw away from the bridge.

"It just kept rumbling for maybe 10 or 15 seconds, it seemed like quite a while. And I was talking on the phone to a friend and I said, 'It doesn't sound good. Something's wrong,'" Wood told CBC News in a telephone interview.

Wood said he went outside to the bridge and saw three or four people gathered there. One man had driven to the edge of the road.

"He was wondering why [an oncoming vehicle] wasn't approaching along the one-lane bridge," Wood said. "He drove up to the bridge and realized there was no bridge there."

The bridge is on Trunk 3 in Tusket. Wood said as far as he knew, no one was on the bridge when it gave way.

In Quinan, where a bridge also collapsed and the road flooded, residents got a break Tuesday as water levels slowly dropped and the rain stopped.

The Tusket Bridge on Trunk 3 collapsed on Tuesday evening. (CBC)

About 50 families left Quinan, which is about 25 kilometres north of Yarmouth. They likely won't be able to return to their homes until the weekend.

Officials were continuing to keep a close eye on water levels at Nova Scotia Power dams on the Tusket River and Lake Vaughan, said Rick Janega of the Emergency Management Office.

"We're still operating within normal levels but the rain that's upstream, yet to come down, will be higher than what we've seen in the past," Janega said Tuesday.

"We've experienced conditions that have been pretty extreme before and we're going to stick with it until the work is done."

Residents survey damage

Bill Muise, a lifelong resident of Quinan, left his home at the height of the flood during the voluntary evacuation on Monday. On Tuesday, he set out in a canoe to survey the damage to his home.

Bill Muise, a lifelong resident of Quinan, took a canoe to survey the damage to his home on Tuesday. (CBC)

"It will probably be close to a month before we can move in because we've got to drain the well and put Javex in that and put Javex in the foundation and stuff like that," he said.

Muise's home sits at the juncture of the Quinan and Tusket rivers. The Tusket, a major river system in Yarmouth County, has numerous branches and associated rivers and flows through a series of lakes.

There is at least one metre of water in Muise's basement.

"I had two furnaces, oil and wood. I have a hot water heater. The pump. Swimming pool that we put up in the summertime, stuff like that. It's all gone," he said.

"This could happen again this spring coming, depending on the snow and rain. But you know, it's an ongoing thing."

Leland Anthony, the Yarmouth district warden, said if water goes over the top of any of the many dams, more bridges and roads could be damaged.

"This emergency is far from over, even though it seems to be fine weather," Anthony said. "It takes a couple of days for all the watershed areas to dump its water into this lake system. This isn't over for us for the next three to four days."

While the dams are still handling the capacity, he said more water is coming into the lakes than can flow out.

Halifax-area bridge closed

A bridge at the Head of St. Margarets Bay on Highway 3, near a Nova Scotia Power station, was closed Tuesday morning because of damage to the concrete.

Cpl. Scott MacRae of the RCMP said the bridge, which is one kilometre south of Upper Tantallon, is no longer safe and is closed until further notice.

"The RCMP are working closely with our provincial partners in the Department of Transportation and Infrastructure to assess the situation," he said. "For the time being, we're advising the travelling public to avoid the area. The road is closed at that section of the highway."

Motorists will have to use Highway 103 until the bridge is deemed safe to reopen, MacRae said. It's not clear how long it will take to fix the bridge.