Scientists are warning that an army of species from Turkey and Ukraine is poised to invade Britain's waterways.
One organism, the quagga mussel, was discovered in a river near London just weeks ago.
At least 10 others are established in the Netherlands and there is a "critical risk" of them coming here.
Researchers are also concerned that invaders, including the killer shrimp, will rapidly spread and devastate native species.
The research has been published in the Journal of Applied Ecology.
In the study, the team from the University of Cambridge looked at 23 invasive species that originate from the waters of the Black, Azov and Caspian seas.
They believe these creatures have spread across Europe in recent years because of canal construction that has helped them move outside their native range.
At least 14 of the species are now well established in the Rhine estuary and in Dutch ports. Four, including the bloody red shrimp, have recently crossed the Channel and established themselves here. Others are likely to follow.
According to the authors, Britain faces an "invasional meltdown".
"I think we are at a tipping point," said Dr David Aldridge, the report's co-author.
"We've been watching species heading our way from the Ponto-Caspian region for the past 20 years or so. They are all building up in the Rhine system just over the ocean.
"We think that particularly now that the quagga mussel has just arrived, we are about to have a big meltdown."
Dr Aldridge confirmed the discovery of the quagga on the Wraysbury River earlier this month.
This mussel smothers native species and causes immense damage by blocking water pipes, and fouling boat hulls and lock gates.
As well as mussels, natives organisms are also under threat from invaders with frightening titles, including the killer, demon and bloody red shrimp.
The invasive actions of many of these species are enhanced because of inter-species interactions.
"Killer shrimp really benefit from the zebra mussel," said Dr Aldridge.
"It gets nice shelter from living between them and also feeds on their waste product. It is such a close association that the shrimps even have a body curve and striping pattern that mimics the zebra mussels, so they can really hide very nicely among their co-invaders."
These mutual benefits continue up the food chain, with larger species such as the goby fish following the path of the shrimps. These bottom-feeders pose a significant threat to UK natives, such as the bullhead, which is already under serious threat.
The researchers say that as well as ballast water from ships, the species often travel in ornamental plants.
However, international water sports events and angling also play their part. Many of the organisms can survive for weeks out of the water in damp locations.
The areas at greatest risk of multiple invaders include the rivers Great Ouse, Severn, and Thames. However, the whole of the UK is under threat.
"Very soon we'll look in any bit of water in the UK and find that actually 90% of the biomass is non-native organisms - that is what it's like in parts of western Europe already," said Dr Aldridge.
"I think we are at the start of a very slippery slope," he added.
The threat from the invaders is not just to the native species. It can have a significant economic impact as well.
"Invasive species - such as the quagga mussel - cost the UK economy in excess of £1.8bn every year," said Sarah Chare, from the UK Environment Agency.
"The quagga mussel is a highly invasive non-native species, affecting water quality and clogging up pipes. If you spot one then please report it to us through the online reporting form."
The researchers' models show that four species are likely to have established themselves in the UK even though they have not been officially confirmed as yet.
What worries scientists is the increasing speed with which these creatures are moving. At the beginning of the 20th Century, it took up to 30 years for a species to move from the Netherlands to the UK. In the past decade, this has reduced to five.
"Due to globalisation and increased travel and freight transport, the rate of colonisation of invasive species into Britain from the Netherlands keeps accelerating - posing a serious threat to the conservation of British aquatic ecosystems," said co-author Dr Belinda Gallardo, now based at the Doñana Biological Station in Spain.
"Cross-country sharing of information on the status and impacts of invasive species is fundamental to early detection, so that risks can be rapidly assessed. A continuing process for evaluating invasive species and detecting new introductions needs to be established, as this problem is increasing dramatically."
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