One of the most popular theories is that there might be a Jurassic-age reptile or population of Jurassic-age reptiles, such as a plesiosaur present in Loch Ness.
Unfortunately, we can't find any evidence of a creature that's remotely related to that in our environmental-DNA sequence data. So, we don’t think the plesiosaur idea holds up based on the data we have.
We also tested other predominant theories of various giant fish; whether it be a giant catfish or a giant sturgeon, an eel, or even a shark such as a Greenland shark. There is no shark DNA in Loch Ness based on our sampling. There is also no catfish DNA in Loch Ness based on our sampling. We can't find any evidence of sturgeon either.
The remaining theory that we cannot refute based on the environmental DNA data obtained is that what people are seeing is a very large eel.
We find a large amount of eel DNA. Eels are very plentiful in Loch Ness, with eel DNA found at pretty much every location sampled – there are a lot of them.
Researchers had earlier suggested that a giant eel might explain some sightings. That idea then lost popularity as theories about extinct reptiles became more common. But there have been ongoing reports of very large eels by a number of witnesses.
Are they giant eels? Well, our data doesn’t show their size, but the sheer quantity of the material says that we can't discount the possibility that there may be giant eels in Loch Ness. We need to investigate more to confirm or deny the theory.