Every year in the second half of August the warm evenings on the Colonnade bridge in Piešťany belong to the mayflies. Visitors of this health resort are often fascinated by this phenomenon, especially when they learn about the specific life cycle and fragile nature of this small insect. Moreover - in contrast to many pictures that capture and emphasize the destruction of the environment - swarming of mayflies proves that in Slovakia, even large rivers, such as Váh are still relatvely clean.