A report of Zebra Mussel Dreissena polymorpha (Pallas, 1771) (Bivalvia: Dreissenidae) in the middle sector of Iskar River, Bulgaria

Single specimens of invasive mussel species Dreissena polymorpha (Pallas, 1771) were found in the middle part of the Iskar River, Bulgaria during 2016 and 2017. A cascade of 14 small HPPs was built in this river sector and a shift in the flowing river conditions with stagnant ones in SHPP dam lakes was induced. Future mass invasion of the species is possible. It is important to provide regular monitoring of occurrence of the Zebra Mussel because of the possible negative economic impact during the invasion