Already high Ottawa River water levels are expected to rise in the coming days as a deluge of spring rain continues.

The levels had been beginning to ease before the rain started Thursday night, but officials fear that's not going to hold. The forecast calls for rain to continue through Sunday, and a rainfall warning is in effect.

Water levels "had been stabilizing in the last day, the last couple days, but the immediate concern, and it's very worrying, is that this rainfall that we're getting now ... the levels will rise again," said Manon Lalonde, an executive engineer for the Ottawa River Regulation Secretariat, which carries out the work ordered by the Ottawa River Regulation Planning Board.

The board manages the Ottawa River basin.

"Saturday, Sunday, into Monday, the peaking time and peaking level, will depend really on the locations ... and this will flood even more homes, so that's the big worry," Lalonde told CBC Radio's Ottawa Morning Friday.

"My heart goes out to people whose houses are underwater. I can't imagine the stress and the hardship that they are going through right now. This is really terrible."

A man kayaks along Voisine Road in Clarence-Rockland on Friday morning. (Andrew Foote/CBC)

Flood warnings, watches issued Friday

The Rideau Valley Conservation Authority issued a flood warning Friday for the Rideau River watershed. Christie Lake on the Tay River is expected to experience flooding as water is released from Bobs Lake to relieve high water there.

Releases from Big Rideau Lake will increase flows downstream. Some flooding can be expected starting on the Long Reach between Manotick and Kemptville, in particular at Hilly Lane, where access roads are expected to be submerged today. Windsor and Brantwood Parks in Old Ottawa South and East, which were under water in April, are expected to be flooded again.

The Mississippi Valley Conservation Authority issued a flood watch for the Mississippi Valley watershed, and a flood warning for Constance Bay along the Ottawa River. Levels are not expected to peak until early next week. Of greatest concern is the Bayview Drive area in Constance Bay, where access could be restricted.

Levels on Dalhousie Lake are expected to get close to the height they were earlier this spring and could exceed those levels by five to 10 centimetres based on the forecasted rain, the authority said. Levels on the Clyde and Fall rivers and on Mississippi Lake are not expected to become as high as they were.

"Water levels remain very high across the upper portion of the Mississippi Valley watershed so it will be at least two weeks before levels begin to return to normal," the authority said.

This type of flooding seen before

The most affected areas are downstream of the Ottawa River's junction with the Gatineau River, Lalonde said, essentially from the Hull Marina to Lac des Deux Montagnes in the Montreal area.

Affected areas include:

Lac Deschênes and Britannia.

Thurso, Que.

Templeton and Pointe-Gatineau.

Masson-Angers.

Clarence-Rockland, Ont.

Grenville.

Hawkesbury, Ont.

Fort-Coulonge, Que.

The Ottawa River basin is managed with large reservoirs north of Gatineau, Lalonde said. While this level of flooding is unusual, it's happened before.

"In a typical year these reservoirs, the way they're regulated, it's so effective at reducing floods downstream that most people don't even realize that there is such a thing as a spring flood," she said.

"But in years like this one, the runoff from the central part of the watershed, the part that is unregulated — so that's south of Maniwaki, south of Lake Timiskaming — the runoff is so great there that the river jumped its bank in some areas, and there are just no man-made structures down here capable of stopping this.

"I have to say that this type of spring flood has been seen in the past in the watershed. It happened in the 1920s, it happened in the '50s and the '70s, and it's happening now. It's just the nature of things, and it will happen again."

In Ottawa, water levels have affected some 75 properties, the city said Friday.

The city has set up emergency reception and lodging centres at the Royal Canadian Legion 616 at 377 Allbirch Rd. and the François Dupuis Recreation Centre at 2263 Portobello Blvd.

'I don't know if we're going to win'

Clarence-Rockland, east of Ottawa, declared a state of emergency late Thursday afternoon. Affected residents are being asked to leave their homes, and a shelter has been set up at the Clarence Creek arena.

"I guess our worst nightmare is coming," Mayor Guy Desjardins told Ottawa Morning Friday.

"We can use all the help we can get, but I don't know if we're going to win on this one. They're saying 30 to 70 millimetres of rain, which would bring the level, they say, to 25 centimetres higher. At 25 centimetres higher we're going to lose a lot of battles, no matter how many sandbags we put in, unfortunately."

More of what Voisine Rd beside the Ottawa River looks like in Rockland, east of Ottawa. One of the many flood zones in the area. <a href="https://t.co/kRcBUKsnWn">pic.twitter.com/kRcBUKsnWn</a> —@amkfoote

The hydro has been turned off on the island where a ferry operates, and natural gas has been shut off to several homes.

The decision to leave, so far, rests with residents.

'Things are tough for many, many citizens'

In Gatineau, Mayor Maxime Pedneaud-Jobin also wants residents to decide for themselves whether they want to leave. Firefighters have gone door-to-door on flooded streets, explaining to residents that there will be delays in the event of an emergency.

"I think it's a personal choice that I do respect," Pedneaud-Jobin told Ottawa Morning.

"Things are tough for many, many citizens. I visit everyday almost every location that is affected, but Pointe-Gatineau, it's terrible because it's not a very rich neighbourhood as well. People are losing a lot. For some people, their house is the only thing they have, so it's difficult for many, many of them."

Residents are boating to their cars this morning on Rue Saint-Louis in <a href="https://twitter.com/hashtag/Gatineau?src=hash">#Gatineau</a>. Could see over 50mm of rain by Sunday. <a href="https://twitter.com/OttawaMorning">@OttawaMorning</a> <a href="https://t.co/k7nGxMnkgX">pic.twitter.com/k7nGxMnkgX</a> —@jessarunciman

Once the rain ends, it will take a bit of time for the water levels to stabilize and then recede, so residents are being asked to prepare to be out of their homes for many days.

"It's sad to say that, but it's not going to be over quickly," he said.