Every year in honor of St. Patrick’s Day the fine city of Chicago dyes the river green. This year photographer Peter Tsai was set up in a Hyatt hotel room to capture the action.

What exactly is used to dye the river green is “top secret” but whatever it is they use 25 pounds of it. Even stranger, it’s orange until it mixes with the water. Either way this fun little timelapse captures the fun and celebration of St. Patrick’s Day.