Under the hull of a container ship that has just docked in a major European port like Rotterdam, Antwerp, or Le Havre, massive tanks have been emptied of thousands of tons of seawater. This water was taken on board weeks earlier in a port in Asia or South America and carried across the ocean. It contains larvae, eggs, and microorganisms that have now been released into European waters. Some of these organisms have survived the journey and have begun to colonize the seabeds and submerged structures of European ports, often without any human intervention being able to stop them. Ballast water from ships is responsible for transferring between 7,000 and 10,000 marine species across the oceans every day. These surviving organisms can establish themselves in new environments, where they often lack natural predators and become invasive species, threatening native species already present in the area. The ballast system is a mechanical process used to stabilize ships. When a ship is empty or lightly loaded, it lacks the necessary balance for safe navigation. To correct this, it takes on seawater into dedicated tanks. This water helps the ship maintain stability, correct its trim, and ensure the propeller functions properly. When the ship arrives at its destination, the water is released to make room for cargo. It is during this de-ballasting process that the ecological risk arises. The few organisms that survive the journey and the release of ballast water are introduced into a new, often foreign ecosystem, where they may multiply and become invasive, disrupting the local environment. According to the International Maritime Organization, ballast water is responsible for the daily transfer of between 7,000 and 10,000 marine species worldwide. This figure is particularly concerning when considering that a single organism can permanently colonize an entire dock. Once established, invasive species are nearly impossible to eliminate. No product or mechanical cleaning of port seabeds can effectively reach populations that have spread across kilometers of docks, piers, and submerged hulls. The port environment provides ideal conditions for these organisms: sheltered waters, artificial structures to colonize, and continuous maritime traffic that keeps bringing new individuals. This creates a self-sustaining cycle of invasion and spread. The problem has worsened over the past few decades due to increased commercial exchanges and maritime traffic, especially with the use of steel hulls, which allow ships to use water rather than solid materials as ballast. The introduction of new species has had devastating effects in many regions, and the rate of biological invasions continues to rise alarmingly. The world's oceans are not separated by physical barriers but are connected through continuous maritime traffic, allowing species to spread easily. To address this issue, the International Convention for the Control and Management of Ships' Ballast Water and Sediments was adopted in 2004. It took 12 years before it officially came into force on September 8, 2017. Since then, all ships making international voyages have been required to manage their ballast water and sediments according to specific rules. Ships must have a management plan, a ballast water record, and an international ballast water management certificate on board. The convention outlines two main standards. The first requires a simple exchange of ballast water in the open ocean, far from any coast, to reduce the risk of organisms surviving the journey. The second, known as the D-2 standard, will eventually require all ships to undergo proper ballast water treatment, which may involve installing special equipment on board. Implementation of these standards is ongoing and gradual. Foreign ships visiting European ports are inspected at least once every three years to ensure compliance with documentation requirements, although these checks are largely administrative rather than biological. The seabeds of several European ports have seen permanent changes in their composition, with mollusks, crustaceans, and algae from other continents now inhabiting areas once dominated by local species. These foreign species can pose serious health, environmental, and economic risks because they often have no natural predators or consumers in their new environments, allowing them to multiply unchecked. Submerged structures, moored ship hulls, and dikes become long-term habitats for these invasive species. Several countries, including Australia, Canada, Chile, Israel, New Zealand, and the United States, have implemented their own national regulations for foreign ships, as have some individual ports. These local rules often preceded or overlapped with the international framework. While compliance with the convention has improved, the seabeds of the ports do not reset to their original state once invaded—traces of these species remain, regardless of future controls.