Swimming and hiking are excellent forms of exercise for dogs. However, as dogs get thirsty, they'll often drink water from any available source, such as a puddle, a pond, a lake, or river.

Usually, these sources won't harm your dog, but it is possible for water-borne pathogens, the same ones that make humans ill, to cause vomiting and diarrhea and other health problems.

Giardia and Cryptosporidium are the two microscopic organisms that are frequently found in outdoor water sources throughout the United States. When ingested by dogs, these parasites can inflame the intestinal tract and cause diarrhea. While most healthy dogs recover from the infection, a case of severe diarrhea can lead to dehydration and a serious illness. Often, puppies, older dogs, and dogs with compromised immune systems are at the greatest risk.

A less common but more dangerous illness caused by contaminated water is known as leptospirosis. Dogs and humans who are infected may experience fever, vomiting, lethargy, kidney and liver failure, and even death. If the disease is suspected, it requires a course of rapid treatment and a course of antibiotics from your dog's veterinarian.

Blue-green algae can appear as foam, scum, or a mat of red, green, or brown algae. If your dog drank contaminated water and shows signs of a skin rash, vomiting, diarrhea, dizziness or stumbling, seek veterinary care immediately as algae can damage the kidneys, liver, intestines, and nervous system of dogs.

Better Safe Than Sorry

While dogs aren't usually in a lot of danger when they drink from lakes and streams, it is better if they avoid drinking from these sources. While it is not always possible to stop a dog from drinking fresh water, the less that they drink the better.

Avoid obviously contaminated water, or water that smells bad. Consider bringing water for your dog when you go camping, backpacking or hiking, especially in areas known for having high levels of infectious organisms.