Last year my two little Yorkies came-down with terrible diarrhea, for no apparant reason. I called the Vet and she asked if we'd been to a lake or camping in the last couple of weeks. As a matter of fact, we had been camping at a local Missouri river, the week before.
She said they had Giardia, a nasty parasite. They can get it drinking from lakes, streams, or rivers. Evidently, it's the same thing as "Montezuma's Revenge", in humans. I always knew humans shouldn't drink that water but I thought animals had a natural defense. I guess not!
The only treatment was Imodium or any type of diarrhea liquid treatment, for several days, until the diarrhea stopped on it's own.
In addition, we had to treat everything in the house and yard and the SUV with a quat sanitizer (Iodine solution). Evidently, bleach and some disinfectants don't work on the parasite.
The next time we camped was at Buffalo Point on the Buffalo River in Arkansas. They had information posted at the fee station on Giardia in dogs. I thought that was a good idea and wish more campsites would post such information.
Anyway, now we always make sure the dogs have plenty of water to drink before we take them to the lake or river and take a bottle of water and a drinking vessel with us.
Hope this saves all of you dog lovers a lot of pain and trouble.
http://www.vetinfo.com/dgiardia.html