Stop, before you step in. If the water is anywhere near outlets, extension cords, or your electrical panel, cut the power to the basement first or stay out entirely. Then shut off the main water valve if the flood is coming from inside the house, a burst pipe or a failed hot water tank. Take photos from the stairs. Lots of them. Your insurance adjuster will want to see the loss before anything was moved.
Then call a restoration company, not tomorrow, tonight. Water keeps working after it stops flowing. It wicks up drywall, soaks into subfloor, and gives mold a 24 to 48 hour head start. Nonstop Restoration answers (403) 620-8489 around the clock with a 45-minute response in Calgary, pulling water out and getting drying equipment running the same visit.