Zooplankton, here Daphnia longispina, plays a key role in lake ecosystems, occupying an important place in the food web and allowing the effects of climate change to be tracked. These small filter-feeding crustaceans are found in a variety of ecosystems, including alpine lakes. Alpine lakes are characterized by harsh environmental conditions, including large changes in light and turbidity caused by two periods: an ice cover period, when both UV radiation (UVR) and glacial flour, the main cause of lake turbidity, are reduced, and an ice-free period with high UVR in clear lakes and low water transparency in glacier-fed lakes. As temperatures rise due to climate change, glaciers are melting, creating new, highly turbid lakes. With ongoing glacier retreat, the connection between the glaciers and the lakes will weaken and the lakes will eventually become clear. Such changes in environmental conditions also bring changes in the biotic composition, with the appearance of certain zooplankton species. This study provides details on the new occurrence of Daphnia in two alpine lakes with different turbidity levels (clear Faselfadsee 4 and glacially turbid Faselfadsee 3 with turbidity ranging from ~0.2 NTU during the ice cover period to 3.3 NTU in summer). In an annual cycle, Daphnia were always present in the clear lake, with an average of 142.4 Ind m-3 and a maximum abundance of 613.3 Ind m-3 in September, whereas in the glacier-fed lake no Daphnia were found from June (0.4 NTU, still ice-covered) to August, when turbidity was at its highest, with an average of 3.6 Ind m-3 and a maximum abundance of 33.3 Ind m-3 in October, about 40 times lower than in the clear lake. Daphnia seem to have established themselves in the clear lake, while they still seem to be struggling to thrive in the glacier-fed lake.