Perth (Australia) - Australian Cindy Joli was able to experience something that many people can only dream of: She swam among a group of dolphins . It could have been a fascinating dive if the marine biologist hadn't noticed something cruel in the video afterwards.

Earlier this week, Joli was snorkeling off the coast of the Australian city of Perth when she suddenly encountered several dolphins in the sea. Completely overwhelmed, the marine biologist immediately pulled out a camera and captured the magical moment.

When she later reviewed her footage, she noticed a detail that she had missed while diving in the murky seawater: one of the animals had been severely injured in its tail fin. Joli writes that a fishing line had become entangled in the porpoise's fin and cut deep into the flesh of the propulsion organ.

The injury may have already caused an infection, which can lead to the loss of the tail fin, according to Yahoo News.

Without the organ, the dolphin is severely restricted in its locomotion and can only swim to the surface to catch its breath or escape from predators with difficulty.

"Unfortunately, this is a very common occurrence on our coast. Not just dolphins, but a variety of other wildlife that I have personally seen far too often," the marine biologist writes on Instagram.

Joli would of course have helped the dolphin immediately and put it out of its misery if she had spotted the fishing line during the dive. However, due to poor visibility, she only noticed the injured fin afterwards. A bitter blow for the environmentalist. "It makes me sad," she admits.

"People shouldn't cut fishing lines, they should reel them in [instead]," says Joli in an interview with Yahoo News.

She advises other beachgoers to always take their own garbage with them or pick up what others have left behind. This could "reduce the impact on our wildlife".