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In this study, the heavy metals magnesium (Mg), zinc (Zn), copper (Cu), manganese (Mn), lithium (Li), tin (Sn), cobalt (Co) and selenium (Se) levels were determined in the feathers of Armenian Gull (Larus armenicus), which is a species classified as near threatened (NT) according to IUCN categories. The Gull lives on the islands of Turkey's largest lake, Lake Van. Different levels were detected due to the urban and rural location of the study areas. The highest levels of Mg, Zn, Mn, chromium (Cr), and Li were determined in the Sıhke pond near the city's dumpsite. The lowest levels were determined on Adır island, with the least human factors. While the levels of Co, Se, and Sn were high in the samples taken from Akdamar Island, the lowest levels were determined on Çarpanak Island and in Sıhke pond.

The zebra mussel, Dreissena polymorpha (Pallas, 1771) is considered as a harmful invasive epibiont species for hydroelectric and nuclear power plants as it reduces or blocks water flow in the plant systems. Although D. polymorpha is reported that it cleans the water, increases water visibility, and filters out pollutants, it has likewise negative impacts on the population and size of some fish and aquatic species. In the present study, zebra mussels were observed for the first time. On the narrow-clawed crayfish living in some water sources in Turkey. Specimens were collected from two natural lakes (Çıldır Lake, Eğirdir Lake) and five ponds (Altınyazı Dam Lake, Keban Dam Lake, Küçükçekmece Lake, Karpuzlu Dam Lake, Kadıköy Dam Lake) in Turkey. Attachments of the zebra mussel to the different body parts of the narrow-clawed crayfish were documented in the present study. Cochran's Q test results showed that the numbers of mussels clinging to the different parts of the crayfish varied (P=0.000) (P <0.001). The difference between the holding regions of zebra mussels on crayfish specimens may cause some adverse effects on the host. Particularly the intensive grip on the carapace partially obstruct the movement, feeding, mating, avoiding predators, and shelter. mussel individuals in the pleopodal region may have difficulty holding and transporting eggs. This study is the first report about the occurrence of D. polymorpha on Astacus leptodactylus in Turkish waters.