Originally published in HR E-Zine 2/2017 on page 13."Why does ballast water pose a danger to eco-systems? Human-mediated introductions of species in habitats outside their native range is a dynamic and non-stop process of global concern. Everyday organisms representing different taxonomic groups are massively transported to large distances in ballast tanks and in a ship’s hull. What is worrying, the scale of this process has significantly increased over the last decades due to a rise in volume of world seaborne commercial traffic and trade. The origin of newcomers in European seas is highly concurrent with major shipping routes where we can find mostly species inhabiting the Atlantic coast of America, Indo-Pacific and Ponto-Caspian regions. Of course not all species are able to survive the journey and establish a self-sustaining population in a new environment – the introduction of newcomers is more likely to be successful in environments that are similar to those of their origin; this means if the port of loading and port of discharge are ecologically comparable, the risk of a species introduction is relatively high. Growing in abundance and expanding its range, the population of non-native species may pose a threat to biodiversity (e.g. through competition, predation, hybridization, transition of diseases, alternation of habitats) and human health, as well as economy (e.g. through outbreaks of serious diseases, infrastructural damages, change of existing fishing patterns, damage to fishing gear, reduction in access to recreational resources). Only then does the non-native species become invasive non-native species. Unfortunately, due to the fact that invasiveness might be determined by different factors, all these unwanted impacts are usually unpredictable. Moreover, they are also almost always irreversible. Hence, it is important to take measures to reduce the number of new introductions. For the reason that eradication of new species is practically impossible in the marine environment and post factum management of invasive species is not easy and costly, the only reasonable alternative that should be prioritized seems to be prevention in the form of ballast water management procedures. Therefore, it is expected that the implementation of International Convention for the Control and Management of Ships Ballast Water and Sediments will significantly decrease problem of invaders in marine ecosystems."