CHICAGO—Hazy, smoke-filled skies from raging Canadian wildfires hovered Wednesday over the U.S. Midwest and East, where millions of Americans were urged to limit outdoor activities as the poor air quality made for dangerous, unhealthy conditions. Much of the Midwest—from western Iowa through Illinois and Wisconsin and into Michigan and Ohio—was under an air quality alert…

CHICAGO—Smoke from raging Canadian wildfires hung over the U.S. Midwest and parts of the East Coast on Wednesday, creating hazy skies and worsening air quality, making for dangerous, unhealthy conditions for millions of Americans. A wide swath of the Midwest, reaching from western Iowa through Illinois and Wisconsin and into Michigan, was under an air…