Every day, more than 7,000 different marine species are transferred to different ecosystems via ballast water in ships. The introduction of invasive species can cause problems for native species. After realizing the serious potential problems associated with the transport of organisms in ballast water, national and international regulations were developed. In 2004, the International Maritime Organization introduced the International Convention for the Control and Management of Ships' Ballast

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... er and Sediments. With these regulations, the problems caused by ballast water have attracted attention and many companies have started to research and develop technologies for the management of ballast water. Today, there are hundreds of different systems for ballast-water treatment, and the selection of the most suitable system for a specific vessel is an increasingly important issue as the Convention nears enforcement on September 8, 2017. The goal of this study is to demonstrate that the application of key performance indicators (KPIs) to the selection of a ballast-water treatment system (BWTS) leads to a very useful tool with which shipyards can compare BWTSs. This allows them to make better choices and to designate the most suitable system for each of their ships. In this study, we examine two types of vessel from a shipyard in Istanbul, Turkey. They have different ballast-water capacities and equipment, and the most suitable system for each is selected by using the KPI method.