Releasing pet goldfish into a pond or lake before the summer break may seem kind, but it is illegal and devastating for native wildlife.
Scientists warn that the common brown frog disappears almost immediately once goldfish arrive, as its eggs and larvae are eaten.
Dragonflies, snails and other native amphibians follow.
Several German-speaking cantons have launched awareness campaigns, while Suisse Romand is relying on case-by-case warnings posted near ponds.
Once the fish are established, options are limited: net or electric fishing can thin the population but rarely clears it.
Scientists say the best fix is convincing owners not to dump their fish in the first place.
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