A playground in Medicine Hat, Alta., is sumberged after heavy rains caused severe flooding in southern Alberta. (Brian Labby/CBC)Many southern Albertans woke up to a soggy mess Saturday after torrential rains hit the southern Prairies, forcing some stranded residents to be rescued from their homes by boat or helicopter.

Several communities remained under a state of emergency and will likely seek aid from the province to help residents recover.

About 20 homes were evacuated in Irvine, Alta., where up to 150 millimetres of rain fell, according to some estimates.

About 200 people were told they should leave their homes in a low-lying area of Medicine Hat, Alta., on Saturday as creeks overran their banks. Water also backed up through drains, gushing along major city roadways and crept close to houses in the city in southeastern Alberta.

Ronald Robinson, the city's fire chief, said the water levels in the South Saskatchewan and its tributaries are not expected to ease until Monday.

RCMP Const. Jeff Waites spent part of Saturday morning getting people out of a rural home in an area 10 kilometres east of Medicine Hat, saying it appeared as if their house was in danger of toppling into the swollen waters of Ross Creek.

After days of torrential rain, the normally dry creek has become a raging river and the rushing water is pushing at the foundation of the home, which Waites described as an estate property.

Ray Gradwell, deputy fire chief of Cypress County, said emergency workers were worried that if the house were swept into the water, it could strike a nearby bridge on Highway 41 — the main detour route being used by motorists travelling between southern Alberta and Saskatchewan.

"If this bridge goes, there's no traffic east-west," he said.

Waites said he was checking on the integrity of the bridge when he looked over and saw the house surrounded by water and people hauling appliances outside.

"[I] realized that the river was potentially washing the house away, so we wanted to clear the people out of the property before that house went into the river," he said.

Rushing waters were lapping at a corner of the home, and emergency officials weren't sure if the running water was making it unstable, Waites said.

Red Cross involved

Leila Daoud of the Canadian Red Cross said 12 homes in Medicine Hat were evacuated Friday and several more families were preparing for more flooding over the weekend.

"We have word from our volunteer teams on the ground that they are now doing pre-evacuation notices of an area in Medicine Hat called the Flats," Daoud said.

"We have a volunteer team that is going door to door with pre-evacuation notices letting people know that they are now on alert."

Red Cross staff are providing emergency shelter, food and water in the Medicine Hat Arena, she said.

Water levels in the area had dropped by about one metre by Saturday morning, but Colin Lloyd, an official with Alberta's Emergency Management Agency, said the "little bit of respite" was not likely to last long, with another low-pressure system expected to move in Sunday.

In addition, forecasters were expecting the heaviest of rain from the incoming system would come Tuesday, meaning some communities might have troubles late in the week.

Highway closed, rivers rising

The flooding has also closed the Trans-Canada Highway for several kilometres on both sides of the Alberta-Saskatchewan boundary, forcing motorists to take a 200-kilometre detour.

The evacuation centre at the Medicine Hat Exhibition & Stampede Grounds. (Bryan Labby/CBC)Additional updates were expected Saturday. Travellers were being advised to check the Alberta Motor Association's website for the latest conditions.

Meanwhile, a high-water warning was issued Friday for the Bow and Elbow rivers in Calgary.

Officials said water levels in the rivers were expected to climb because of runoff from melting snow in the Rocky Mountains, combined with the heavy rains.

The Calgary Fire Department recommended people stay away from the waterways.

With files from The Canadian Press