The majority of the world's freight is transported by sea, with more and more ships taking goods to developing countries like India and China.
However the cargo ships are unwittingly transporting larvae and tiny organisms that could cause damage to other species. This is because cargo ships take up water for ballast once they have discharged their load. When they arrive at the new destination the water is dumped - along with any living stowaways on board.
Over the years ships have transported comb jellyfish from the US to the Black Sea, where they have decimated fish stocks. The European green crab has caused problems in the US and Australia and Asian kelp has caused havoc in New Zealand, Europe and Argentina.
In the UK the Chinese mitten crab and European zebra mussel are just some of the invasive maritime species transported by sea threatening native species.
It is estimated that up to 10 billion tonnes of ballast water is transferred globally each year.
Participants in the Volvo Ocean Race are currently taking tests from waters around the world to gauge the scale of the problem.
Friends of the Earth say it is a "ticking time bomb" that could cause serious damage to major ecosystems beneath the waves. Although many of the organisms transported are very small it can have a knock-on effect that damages the fish stock and ultimately other life - including humans - that rely on the sea.
The International Maritime Organisation is calling on every country in the world to sign up to the International Convention for the Control and Management of Ships' Ballast Water and Sediments that would require ships coming into port to clean the ballast before entering.
So far 60 countries have signed up - but not the UK.
Jim Fitzpatrick, the shipping minister, said the Government was supportive of the idea and working hard to improve the situation.