It's the dead of night.
And while the rest of the world sleeps, a team of scientists is wading knee-deep through the fast-flowing streams that cut through the Pyrenees.
I've joined them on the trail of a creature that few have heard of and even less have set eyes on: the Pyrenean desman (Galemys pyrenaicus).
This small aquatic mammal only comes out under the cover of darkness. And it's not easy to find.
Half-submerged in the dark waters lie several tube-shaped mesh traps; the hope is that a passing desman may have swum into one.
The researchers angle their head torches for a closer look. But most of the traps - apart from the odd trout that has sneaked in - prove empty.
The desman was once thought to be widespread across mountain ranges in France, Spain and Portugal.
But now Catalonia's Alt Pirineu Natural Park is one of the last strongholds for this species.
And eventually, we strike lucky: inside one of the traps, a glint of grey catches in the beam of a torch.
As the researchers gently remove the creature from the stream, I'm able to take a look at the odd little mammal.
At first glimpse, it looks like a strange mish-mash of creatures - part rat, part mole, part platypus.
It's about the size of a hamster, with a glossy grey coat.
It has a huge nose - like a miniature version of an elephant's trunk - framed with long whiskers and beady little eyes. Its front paws are tiny, but its back feet are huge - and webbed. It's topped off by a thick, scaly tail.
"It is such a special creature - it really is one of Europe's strangest creatures," says Dr Yolanda Melero, who is based at the University of Aberdeen but is working with the University of Barcelona to carry out desman research.
"It's very well adapted to its environment: it is a very good swimmer."
Very little is known about the Pyrenean desman. But this team of researchers is trying to change that to answer some of the most basic questions.
"The first thing we are trying to find out is their distribution: to see how many there are and where they are," explains Dr Melero.
"There was some data collected in the 1980s and 1990s, but this isn't reliable."
Wildlife biologist Pere Aymerich, who works with Joaquim Gosalbez from the University of Barcelona, says there has been a dearth of research partly because the creature is so tricky to study in the wild.
"They are very difficult to see due to their nocturnal activity and aquatic habitat," he explains.
But this team is getting better and better at tracking down desmans in the wild, and their research is overturning some commonly held beliefs about the animal.
Mr Aymerich explains: "We conducted a study based on radio-tracking, and we were surprised that our results on behavioural aspects and social relations of the desman did not coincide with what had long been assumed to be correct: the desman is not an aggressive, solitary and territorial animal, but is tolerant with other individuals of the species and seems quite sociable."
Last in line
One reason that the team is trying to shed more light on this creature is because it provides a window into our ancient past.
Millions of years ago, there were many aquatic species just like the desman - all belonging to a group of animals known as the Desmaninae.
But now, the Pyrenean desman is one of the very last in its evolutionary line. Only this species, and a creature called the Russian desman (Desmana moschata), which is larger and furrier than its Iberian counterpart, are left.
Jose Castresana, from Barcelona's Institute of Evolutionary Biology (CSIC-UPF), explains: "This is a relic species - for some reason only these two species survived."
While much of the behavioural research takes place in the dead of night, during the day the field work takes a less glamorous turn, and Dr Castresana spends the time looking for desman excrement.
He explains: "If they are fresh, then we can extract the DNA. This is an extraordinary species - its genetics has not been very well studied until now."
The researchers are keen to build up a clearer picture of the desman. This has been driven by the fact it may be under threat.
"Although the data is scarce and difficult to compare, we know of some places where the desman has disappeared," says Dr Castresana.
"One area is in the southern part of its distribution - there for sure, it is endangered or almost extinct. Our data also indicates that there are some other places where it may be slowly disappearing as well."
Changes to the streams and rivers, such as the construction of dams, are thought to have an impact on the small invertebrates that the desmans feed on. Some studies also suggest that the creature may be particularly sensitive to water pollution.
This, says Juan Fernandez, a biologist at the Alt Pirineu Natural Park, makes it all the more important to safeguard the areas where the creatures are doing well.
"We have an important habitat - mountain rivers and fast-running, clean waters, rocks and a lot of macroinvertebrates for the desman," he says.
"For us, it is wonderful to have this marvellous creature in the park. But it is also a big responsibility to protect this animal because we have one of the best preserved populations in all the distribution area"
Back in the mountain stream, the scientists' work is done and they are ready to return the animal to its watery home.
These researchers are doing everything they can to shed light on this creature - they say that this is the key to safeguarding the future of this unique species.
Mr Aymerich explains: "To conserve or save any species, it is essential to know how it 'works' and interacts with the environment.
"It is only with this information that we can plan a proper conservation plan for this rare and singular species."