My Dog Has Scabs All Over His Body, What's Wrong?

Sounds like he has either an allergic reaction to fleas, a pet shampoo or flea medication or maybe even a condition called Mange. I would consult a vet right away or purchase a home remedy book on pets. I have one and use it very often as I have 3 dogs.
Good Luck- Auntimaime

Did your dog go into the water?  I'm wondering if there wasn't something in the lake water that caused this.  I'd sure take your dog to the vet.  It can't be comfortable, yet some dogs are quite stoic and will not complain.

It might have mites they get under the fur ,thats when the dog will scratch,and it would make them bleed, we call it mange. Try dirty oil and sulphur. Rub the sulphur on his body then put the oil on. The yellow sulphur will kill the mites or mange, and the oil will stop him from licking it off. Be careful ,don't put y/s on or near his face. Just use the oil there.

I was thinking that your dog is allergic to fleas, but in your question you make it sound like he got scabs all over his body in just two days.  That sounds a little unrealistic.  Did he not have scabs before you went to the lake?  If he did, then I would still lean towards the flea allergy and you should treat him for fleas.  What you can do is take  him to the local vet and ask for some flea medicine, the kind that you rub between the shoulder blades.  It's about 12-15 dollars and I think it last three months.  Anyway, while you are there at the counter purchasing the medicine you can ask if they think the scabs are from fleas.  Most vet offices will tell you what they think at no charge to you.