Freshwater jellyfish spotted in Belgrade lake, experts say they are harmless

An unusual sight has appeared in Belgrade's Ada Ciganlija lake: freshwater jellyfish. The presence of these creatures in the popular urban swimming spot has surprised many residents, who typically associate jellyfish with marine environments.

However, experts have reassured the public that there is no cause for alarm. The jellyfish observed in Savsko lake are a species of freshwater jellyfish, Craspedacusta sowerbii, and are entirely harmless to humans. They are known to appear during warmer months when conditions are favorable, indicating a rich and interesting underwater ecosystem within Ada Ciganlija.

These jellyfish prefer warm, stagnant waters, making the artificial and relatively shallow Savsko lake an ideal habitat, especially as it heats up quickly during summer. Their appearance is tied to water temperatures reaching around 25 degrees Celsius or higher. At these temperatures, tiny polyps develop into the visible jellyfish form that floats near the surface.

While they possess stinging cells used to capture small plankton and microorganisms, these cells are too weak to cause significant reactions in humans. Most swimmers will not even notice them, and any contact typically results in a barely perceptible sting or very mild irritation for particularly sensitive individuals. Their appearance may be striking, but it poses no threat to swimmers.