Up to 100 millimetres of rain have drenched southwestern Alberta since Wednesday and more is forecast on Friday.
Volunteers in Cardston, more than 200 kilometres south of Calgary, spent most of Thursday sandbagging to protect businesses and homes from swelling Lee Creek, which runs through the town.
Steady rain in the past few days has created high groundwater and high flows in the creek, which are taxing storm sewers, said Jeff Shaw, the town's assistant administrator.
Cardston has absorbed 84.6 millimetres of rain since Wednesday morning, exceeding the 82.6 mm it normally sees for the whole month of June, according to Environment Canada. Another 50 to 60 mm of rain is expected on Friday.
No evacuations have been necessary so far, said Shaw.
Reserve declares state of emergency
About 40 families are stranded on the Blood Tribe reserve, which declared a state of emergency at 2 p.m. MT Thursday.
Emergency crews are working to bring families food and water, said Oscar Cotton, the reserve's director of disaster services.
Some highways and roads on the reserve have been closed.
A flood watch — which means streams may overflow their banks — has been issued for Lee Creek, the St. Mary River downstream from the St. Mary Dam, and the Waterton River downstream from the Waterton Reservoir.
A high stream flow advisory was in effect for the Oldman, South Saskatchewan and Milk rivers. That means water levels are expected to rise rapidly but no major flooding is expected.
"We're asking people to be cautious around the creeks, the waterways in the area," said Carrie Sancartier of Alberta Environment.