Calgary road crews have been busy.

In two months, they've fixed 3,500 potholes, the city says.

Calgary went through a hard winter of cold temperatures and lot of snow. A cycle of freezing and thawing created thousands of potholes. Snow melts into cracks in the road, and when it freezes, the cracks expand, creating craters.

The city received about 5,000 pothole complaints, some of which were duplicates.

How do potholes form? Watch this video:

How do potholes form? 0:35

There may have been so many complaints because road crews weren't able to fix potholes throughout the winter this year, Mayor Naheed Nenshi said in a release issued Tuesday.

"Due to extreme cold temperatures, they have been playing catchup to get the work done," he said in the statement. "They are making great progress, but we still have some work to do."

Report potholes, city asks

The city asks residents to report potholes by calling 311 or going online. The city inspects major roads for potholes and fills those first, but relies on complaints for residential area issues.

Calgary has budgeted $6.2 million for "minor asphalt repairs," including fixing potholes. It's unclear how much of that has been spent.

It's also unclear, for comparison's sake, how many complaints were received about potholes in the same time period in 2017. But the city says this spring, they've received a "slightly higher" number than in previous years.