Sevarius came here to capture the Loch Ness Monster and use its genetic material for various unscrupulous breeding projects. Fortunately, Goliath, Elisa, Angela, and Bronx were also brought here on the Avalon World Tour, and foiled his scheme. ("Monsters")
A gargoyle clan has existed at Loch Ness since at least the 10th century, and most likely long before that time. The Loch Ness Clan keeps itself well hidden, however, and had no contact with Goliath and his companions during their visit (although Sevarius initially believed Angela to be a member of it). Its existence may account for Griff's having automatically recognized Goliath in 1940 as being of "Scottish stock". 
Real World Background
Loch Ness is roughly 24 miles long, at least one mile wide, and as much as 754 feet deep. The murky waters of Loch Ness have been explored many times in search of the Loch Ness Monster, but with no official success as yet.
- Loch Ness at Wikipedia, the Free Encyclopedia