Hi Mike, see no one has replied. That's a shame as I'm heading to plockton for family get together in August. I've been doing a bit of research to lochs in the area as I want to take my 4 year old son and 72 year old dad to one (or more depending). I've got my eye on Loch An Arbhair and Lochan a Chaorainn that look like you can car to within reasonable walking distance, and as far as I can see no permission is required (but I'd check just in case). If you have a an OS map then they are 883343 and 895347 respectively. Hope this helps. And Google earth and street view are very handy!
