Many aquatic pests attach to the bottom of ships and get a free ride to their next location. Others make their way into the "counterweight" of a commercial vessel.

WHAT DOES THIS MEAN?

When a ship makes its way across the ocean, it needs to balance its weight. An empty ship needs to take in large amounts of water to weigh it down. Upon arrival at a certain port, it then releases the accumulated water to balance out the heavy cargo. Sometimes, different species of aquatic pests get transported in the process, and released into the waters of this new environment.

Now, vessels are inspected to gain entry into Australian harbours. These can involve internal or external inspections. External inspections involve a visual examination, often with a scuba diver. Internal treatments use chemicals to clean out the area.