Are there water lilies in the Danube? The answer is obvious to anyone who knows that water lilies are not river weeds. Every year since 2012, we have been able to admire the late summer mass migration of this mayfly species, which is related to the Tisza flower, along the Danube. However, no one has yet confirmed its permanent presence on the Budapest section of the river. During our expedition, we will find the answer to the above question and, as a bonus, we will even witness the birth of a new miracle device for saving mayflies.