Invasive Species in UK Quarries: What Divers Should Know

Every summer, as the water in Britain's flooded quarries finally warms past the point of discomfort, dive sites from the Midlands to the South Coast fill up with bubbles again. It's the season most UK divers wait all year for: long daylight hours, decent visibility, and the chance to get properly comfortable in a drysuit or wetsuit before heading off on a holiday abroad. But if you've been diving the same UK quarry for a few seasons running, you may have noticed the underwater scenery changing in ways that have nothing to do with the weather. Populations of non-native crayfish, shrimp and mussels have been quietly reshaping the ecology of British freshwater sites, and as divers we are often the first people to see it happening.

Why Invasive Species Matter in UK Quarry Diving

Flooded quarries are unusual habitats. They were never meant to be lakes: they are old industrial excavations that filled with rain and groundwater once quarrying stopped, and the ecosystems that developed inside them are often fragile, slow to establish and easily knocked off balance. A single new arrival, whether introduced deliberately or by accident, can spread through a closed body of water far faster than it would in a river or the open sea, because there is nowhere for native species to retreat to and no strong current to limit how far larvae or eggs can travel.

For divers this matters for two reasons. First, healthy quarry ecosystems are part of what makes UK diving worth doing between open water sessions and drysuit courses: interesting structure, decent fish life, clear water in the right season. Second, quarry centres and dive clubs increasingly ask visiting divers to help monitor and report what they see, which means understanding a bit of ecology is becoming a genuinely useful diving skill, not just a nice to have.

The Species Turning Up in British Quarries

Signal Crayfish

The signal crayfish, originally from North America, is the species most UK divers will already recognise. Larger and more aggressive than the native white-clawed crayfish, it carries a fungal disease called crayfish plague that is harmless to the signal crayfish itself but fatal to native populations. Where signal crayfish establish themselves, native white-clawed crayfish tend to disappear from that water body within a few years. Divers often spot them tucked under ledges or scuttling across silty bottoms during a torch sweep, and they are now the default crayfish encounter at most inland UK dive sites.

Killer Shrimp

Dikerogammarus villosus, better known as the killer shrimp, is smaller and easier to miss but arguably more disruptive. It preys on native invertebrates, insect larvae and even small fish, and it reproduces quickly in the right conditions. It has spread through several UK reservoirs and quarries since first being confirmed in the country, often carried between sites on wet kit, boats or angling gear that hasn't been properly cleaned and dried.

Zebra and Quagga Mussels

These small striped mussels attach themselves to any hard surface in colossal numbers: ladders, ropes, old machinery, even other shellfish. A single female can release up to a million eggs in a season. Their filter feeding can genuinely change water clarity, which sounds like good news for visibility until you consider what it means for the plankton and food chain underneath, and their sharp shells can be a real hazard to bare skin on entries and exits.

How These Species Get There, and Why Divers Are Part of the Story

Almost none of this spread happens on purpose. Invasive aquatic species move between water bodies on damp equipment: a wetsuit boot, a BCD bladder, a length of rope, a boat trailer. Larvae and juvenile mussels can survive for days in a few millimetres of water trapped in a valve or a fin strap. That means the same divers who care most about UK sites are also, without realising it, one of the more efficient ways these species travel from one quarry to the next.

The good news is that the fix is simple and already familiar to most divers as basic kit care. The Check, Clean, Dry approach, promoted by the Great Britain Non-Native Species Secretariat, asks divers and other water users to check equipment for animals or plant material after every dive, clean it thoroughly, and dry it completely, ideally for at least 48 hours, before using it at a different site. It costs nothing and takes a few extra minutes at the car park.

What Responsible Divers Can Do

Beyond kit hygiene, there is a lot ordinary divers can contribute. Many UK quarries now support citizen science recording schemes, and a five minute report after a dive, noting what you saw and roughly where, genuinely feeds into how these sites are managed. A few practical habits worth building into every quarry dive:

Rinse and dry kit between different UK sites, not just after saltwater trips. Photograph anything unfamiliar rather than assuming it belongs. Report suspected sightings to the site operator or through the Environment Agency's invasive species reporting channels. Avoid moving stones, structures or found items between sites, since larvae travel on surfaces as easily as in water. None of this requires special training, just the same attention to detail that already gets taught in an Open Water course: observe first, react second.

How This Connects to Training and Conservation at Diving Academy

At Diving Academy we see UK quarry diving as more than a training backdrop for our Reading based courses. It is a genuine part of the diving we do all year, and the health of these sites matters to us as much as it does to any diver who loves getting in the water close to home. Our Conservation Academy runs specialty courses that go deeper into topics like invasive species identification, citizen science reporting and habitat monitoring, and they are a natural next step for anyone who has finished core training and wants their diving to do a bit more than rack up dive numbers.

We also brief every group heading to a quarry, junior divers included, on basic Check, Clean, Dry practice before they get in the water. It takes two minutes and it is one of the simplest ways a diver at any level can make a real difference to the site they are diving in.

Frequently Asked Questions

Are signal crayfish dangerous to divers? Not really. They can give a sharp nip if handled carelessly, but they pose no serious risk. The concern is ecological, not personal safety.

Should I remove invasive species if I find them? Generally no, unless a site explicitly runs an organised removal programme with proper permissions. Untrained removal can do more harm than good and may be against site rules. Report sightings instead.

Does this affect junior divers too? Yes, and it is a great topic for younger divers precisely because it makes the science of diving tangible. Spotting and reporting an unusual crayfish is a genuinely useful contribution, not just a fun fact.

Do I need special training to help monitor sites? No. Basic awareness and accurate reporting are enough for most citizen science schemes. Specialty courses go further for anyone who wants to get more involved.

Curious about UK conservation diving or want to get involved with monitoring at the quarries we train at? Visit our Conservation Academy or get in touch, we're at Bellman Court, Great Knollys Street, Reading, or call +44 (0) 118 9761 729.