Dogs are one of the largest spreaders of giardia (See: Aukerman & Monzingo. Nov. 1989, “Journal of Forestry.” pp. 18-21.). When hiking around springs, don’t let your dog wallow (or poop) in or near the water. “Next to humans, dogs appear to be the largest spreaders of Giaridia (p. 18).”
Dogs must be on a leash at all times in National Parks. It is quite disconcerting to see dogs running loose and chasing wildlife. Another problem, particularly in the morning and evening, is rattle snakes. My son’s dog was struck and required about $500 of anti-venom (this was at his house in Utah).
Three days ago I camped at Emigrant Ranger Station campground. A fellow had two beagles, which he kept on leashes. They barked constantly in the evening and began again at 6 am. I asked the fellow to quiet them and he refused. If I had a roll of duct tape, I would have taped their mouths shut.