If you're bringing the filter...
Posted by: pikabike on Dec-29-12 7:36 PM (EST)
...then it'd be foolish to not use it, no matter where in the lake or river you are. Water moves around.
Giardia is known to be in all 50 of the United States. I suspect I had it one time, and the illness took a full month to leave me feeling halfway normal. If you don't want to filter, you should boil the water. You will need to boil it for a certain amount of time (I forget what it is), not just bring it to a boil.
Beware one thing about crypto: Iodine does NOT kill cryptosporidia organisms. In 1999 my husband and I were car-camping and mountain biking in southwestern CO. The first and second nights, we camped at a campground with well water. The water gushed out silty and ruddy-colored, with the strong and distinctive taste and odor of iodine. The area had received abnormally high rainfall the weeks before we arrived. We drank that well-water, unfiltered. After a day or two, we both felt nauseous. Did not make the connection at the time. There's a photo of me taken on the trail looking pale and slightly green. The sick feeling did not go away for at least a week afterward. I later read that iodine is ineffective at killing cryptosporidia. The well-water must've been contaminated.
It's not worth skipping the effort to filter your water.