If you find the published information about Giardia confusing and inconsistent, it’s because the information is a reflection of the parasite itself. Giardia is a multifaceted protozoan that affects individuals differently. It can be prevalent in one small corner of a lake, and practically absent in other parts of the same body of water. In the context of backcountry water, cases of Giardia are rarely diagnosed or reported and there haven’t been enough scientific studies to understand the risks to backcountry travelers. To further complicate the matter, the symptoms of Giardia are difficult to distinguish from those of cryptosporidium, another parasite.