Why does my dog have diarrhea?

Beware... These are gross details. I adopted a 1 year old beagle from the humane society 2 weeks ago. There have been no issues. Today when I let him out of the crate he had diarrhea. I noticed (on my white carpet) that is was the consistency of mucus. I was matted with grass and snot like goo. It was so think that when i picked it up with a wash cloth the rest dangled from the rag. Gross! There were steaks of red like blood mixed in the brown goo. He and my other dog have been lore laid back than usual. Neither ate their dinner. Both dogs are up to date on everything. Is this a vet emergency?