Loch Ness is giant ‘spirit level’
It is a tiny signal seen in the way the waters at the ends of the 35km-long lake rise and fall.
When combined with the direct tug from the gravity of the Moon and Sun, the loch surface goes up and down by just 1.5mm.
The study is reported in the Journal of Geophysical Research.
"If you were on a boat in the middle of the loch, you certainly wouldn't notice it," said Philip Woodworth from the UK National Oceanography Centre (NOC), Liverpool, "but a tide like this has never been observed in a western European lake before."