"Dear tourists, we respect you. It's time for you to start respecting yourself. So, stop making stupid and dangerous selfies. Thank you," the service said on Twitter.
The appeal came after the young Canadian plunged off a 75-metre (250-foot) viewpoint in the Plitvice Lakes national park while trying to take the perfect selfie.
The 20-year-old miraculously survived, as tree branches broke his fall, but he sustained serious injuries, police said.
Last year a 54-year-old Slovak tourist was killed when she fell from a rock in the same national park, also while trying to take a photo.
Tourism is a key sector of Croatia's economy, and last year the country of 4.2 million people welcomed more than 14 million visitors, with most heading to its pristine Adriatic coast.
Get a selfie stick.
