"We've provided an evacuation centre for people who need to get out of their homes right now," said Claresholm Mayor Rob Steel.
Overland flooding in the town of 3,800, about 130 kilometres south of Calgary, had affected about 40 homes and some sewers were starting to back up.
Steel said the only formal evacuation order was for the town campground, but some residents needed help right away. Some homes were surrounded by water and some were actually submerged.
There is no river nearby. The nearest waterway, Willow Creek, is at least five kilometres from the main townsite.
It has been raining off and on since Monday afternoon, but Claresholm's problems started after a heavy downpour early Wednesday that one town official described as "coming down in sheets."
"We need the rain to stop," Steel said. "Our infrastructure is very good here, but it's not keeping up."
Those whose homes were affected were being offered shelter at the arena. The fire department was helping those who couldn't make it on their own.
"We're asking everyone else to just stay off the streets," said town spokeswoman Karine Wilhauk. "We're just trying to deal with this situation. We don't want to have any more problems."
All schools were closed but students writing diploma exams were being bused from the evacuation centre to their schools. Town officials said water levels appear to have stabilized, but a heavy rainfall warning remains in effect.
Many communities in the area have received over 90 millimetres of rain. Environment Canada is predicting another 40 to 70 millimetres in southwest Alberta before the sun returns on Friday.
The flooding comes as Alberta prepares to mark the one-year anniversary of the 2013 flood. In total, 100,000 people had to flee their homes in southern Alberta last June.
Communities hit the hardest in that flood — including Canmore, Calgary and High River — are further to the north of the area currently experiencing high water and are fine so far.
Claresholm Resident Phyllis Faulkner told radio station CHQR she watched as water poured into her basement, just as it did last year.
"I'm standing there. The water's running in and I'm screaming at the top of my lungs, going, 'I can't stop it. I can't stop it,'" she said.
"I'm going to lose everything again — my brand-new furnace is under water again. My brand-new hot-water tank is under water again.
"They're done. They're toast."
The Blood reserve, the town of Cardston and Lethbridge County were also preparing residents for possible evacuations due to rising river levels.
States of emergency were also in effect in Coalhurst, the Municipal District of Willow Creek, Crowsnest Pass and Medicine Hat, where the city was advising residents in a handful of neighbourhoods that they might have to leave their homes in the next 48 hours.
Medicine Hat fire chief Brian Stauth said he was "more optimistic" Wednesday because there was less precipitation than expected to the west. Some of that fell as snow, which will have less impact on river flows, he added.
But he warned river levels will still rise. Water levels aren't expected to peak in Medicine Hat until Friday.
"Unless information changes, our current planning for flood mitigation measures remains in place. We want to err on the side of caution and take any steps required to protect life, safety and property," said Stauth.
The city said it was expecting fewer evacuations than 2013 when about 10,000 people had to head for higher ground.
"All we're asking people to do at this point in time is prepare themselves in case they need to leave on short notice," said Stauth. "Gather any important documents they might want to take with them. If they so choose ... move anything important from a lower level to an upper level in their home."
In the city of Lethbridge, there was no state of emergency, but people were being advised to stay away from possibly unstable riverbanks as water levels in the Oldman River continued to rise. Bridges across the river remained open, but sandbagging was underway at the water treatment plant and some other areas at risk.
The river valley was closed to the public.
— By Bob Weber in Edmonton, with files from Jennifer Graham