Elle, YOU are a friendly soul, and well-mannered in your dealings with folk on this forum, but not all are like you.
I would not mind a shilling for everyone who I have helped on here who could not manage a friendly "ta"!
The smallest loch? I have not the faintest idea.
The largest, by volume, is Loch Ness, by area, Loch Lomond. The deepest is Loch Morar.
Smaller lochs are called lochans.
So, when does a loch become a lochan?
When is a lochan only a biggish puddle?
There is no formula that I know of, to provide an answer.
However, it is not Loch Nineacht at Dundee, which is what the Google search engines tell us.
No such loch!
The Highlands are full of lochs of all sizes, many nameless.
Is it vegetable plants you shall buy?