Diver on Loch Lomond

Observation - Diver on Loch Lomond - UK and Ireland. Description: No photo I'm afraid. Spotted a pair (although not terribly close together) of divers. Not sure what type as both were in silhouette. Could not see any contrast. I know they frequent sea lochs in winter, but this part of Loch Lomond is not far from Loch L

No photo I'm afraid. Spotted a pair (although not terribly close together) of divers. Not sure what type as both were in silhouette. Could not see any contrast.
I know they frequent sea lochs in winter, but this part of Loch Lomond is not far from Loch Long.
I positive these were not cormorant which also frequent the loch as the bills were more robust looking and neck more stocky. Just not sure which species of diver it would be.