Cute photo! But we could have put a horrible one here, of a lamb torn to shreds by a dog. Sadly, that's all too common at this time of year. The danger in the headline is to the lambs, obviously, not to walkers.
Here's what the Yorkshire Dales National Park website says:
Lambing time can run until June. Keep your dog under close control, preferably on a short lead. Even dogs on long leads can frighten sheep enough to miscarry or lose their lambs.
Humans can have the same effect, so if you're crossing a field and can possibly detour a bit to avoid ewes and their lambs, please do so.
One further, sobering extract from the National Park website:
Remember, a farmer is legally allowed to shoot any dog worrying livestock.