August 9, 2025, 6:05 am | Read time: 5 minutes
Giant predatory fish suddenly shooting out of the water and attacking a swimmer in a lake? What sounds like a scene from a horror movie actually happened: In the Brombachsee in Middle Franconia, two incidents involving catfish caused a stir. These impressive predators, which can grow up to two meters long, are considered the largest freshwater fish in Germany. Do swimmers now have to seriously fear for their safety? Fisheries scientist Robert Arlinghaus from Humboldt University in Berlin explains how such encounters occur–and why panic is completely unfounded.
What Happens Below the Water’s Surface
When you swim in a lake, you enter the natural habitat of fish. Depending on the size and nature of the lake, between 50 and 100 different fish species can be found. “All sorts of species like roach, perch, bream, or even a catfish might swim near you. A pike might also lurk somewhere in the reeds or underwater plants, watching you,” says Robert Arlinghaus, professor and head of the Department of Integrative Fisheries Management at the Faculty of Life Sciences at Humboldt University in Berlin.
Generally, these encounters go unnoticed–mainly because visibility underwater in many German lakes is limited. Additionally, fish are naturally shy. “The animals have a certain avoidance behavior, so they keep a bit of distance from swimmers. At bathing spots, the fish sometimes get used to people and swim visibly around them, especially roach and bleak schools,” Arlinghaus continues.
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How Real Is the Danger from Predatory Fish in Lakes?
Whether pike or catfish–both are native predators that also live in bathing lakes and often make headlines. However, actual attacks on humans are extremely rare. “Fears are completely unfounded. Winning the lottery is more likely than an attack by these fish,” says Arlinghaus.
Pike mainly react to movements on the water’s surface–for example, when a toe dangles from a dock into the water. “If you let your legs dangle from the dock and your toe touches the surface, it has happened that a pike assumes: ‘That’s a fish’–and attacks the toe. But you need a lot of bad luck for that,” the expert emphasizes. Underwater, however, pike are absolutely harmless: “They ignore swimmers and divers and simply remain motionless in the reeds or underwater plants or swim away if it gets too lively for them.”
When Catfish Might Actually Bite
Attacks on humans by catfish are also extremely rare–and almost exclusively tied to a specific time. “Every few years, there are cases where a catfish snaps at a swimmer’s leg. But this can only happen during the roughly two weeks in midsummer when the male builds and guards a nest,” Arlinghaus explains. Even then, attacks only occur if a swimmer accidentally disturbs the nest.
However, such nests are usually far from swimming areas. “The nest is located in protected, dark areas where people usually don’t swim. The catfish doesn’t build its nest on the beach, where it’s flooded with light,” Arlinghaus says. In the case of the Brombachsee, an unusual scenario occurred due to the low water level: “In the specific case at Brombachsee, the shore areas had dried up, where the water had receded–and there were bathing islands. These provide sun protection, which a catfish used for its nest.”
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What to Do if a Fish Bites?
Even if an attack occurs, there is hardly any risk of injury: “If you’re unlucky and a catfish attacks, there are no significant injuries–it’s not a shark with huge teeth. Essentially, the catfish has no teeth, just bristle-like teeth. If it attacks, it’s more of a bump that gives you a fright.”
Experts advise staying calm in such a situation and slowly leaving the water. Even if the shock is great–serious injuries are not a threat. Disinfect small wounds as a precaution and monitor the area. However, if there are stronger reactions, a doctor should be consulted.
How Swimmers Can Be as Considerate as Possible
Even though encounters with a catfish or pike are usually harmless, humans are a disruptive factor in the lake ecosystem. “As soon as you enter a body of water, it’s a certain disturbance. Whether it’s ecologically relevant is another question. It’s poorly studied and is likely only relevant with mass occurrences over many weeks,” says Arlinghaus.
Other influences like trampling damage on the shore or chemical residues from sunscreen could have significantly greater impacts. Particularly problematic is the destruction of underwater plants, which provide important habitats for fish: “A problem is the uprooting of underwater plants and stirring up sediment, which can cloud the water and release nutrients. Therefore, you should keep a distance from large clusters of such plants to avoid dislodging them with your feet. These underwater plants are important fish habitats and are crucial for the ecosystem. So it’s better to enter the water at sandy beaches.”
With material from dpa