Scotland's most compelling tourist attraction is no Jurassic relic, if she - or he - is a permanent resident, and is unlikely to weigh more than 300 kilos (660lbs).
The most comprehensive review for 13 years of the ecology of the loch is to be published shortly in the scientific journal, the Scottish Naturalist. The 13 research papers do not address the Nessie question directly, but their findings on the life of the loch shed new light on what can, and cannot, exist there.
Adrian Shine, head of the Loch Ness Project at Drumnadrochit, believes much of the evidence points to a sturgeon.
Naturalists calculate the total fish population of the loch weighs about 30 tons. Any resident predators would themselves weigh no more than a tenth of that, or three tons in total. A viable population would require 10 predators - making 300 kilos the maximum size for each.
Forget the left-over dinosaur theory. The last plesiosaur was fossilised 65 million years ago, and 10,000 years ago Loch Ness would have been a giant ice cube.
Nor could the monster be an amphibian: Studies have shown that none of the loch's fish are exclusively freshwater. They are either descended from, or still remain, fish that come and go to the open seas, unlike any known amphibian. Nor is Nessie likely to be a mammal, although whales, porpoises or seals could account for some sightings. Deer also swim in the loch.
The first locally-recorded sighting of a monster appears in the Inverness Courier, in 1868. This spoke of a huge fish and local legend has always spoken of a fish-like animal.
Enter the Baltic sturgeon,a big sea-going fish with a reptile-like appearance and dorsal fin set towards its tail which enters fresh water to breed and spawn.
It lives in cold northern waters like the Baltic and rarely ventures into British rivers. It can be three metres long or more and weigh 200 kilos. 'It is my favourite of the current theories,' Mr Shine said. 'But it would be rather nice to think I am wrong.'