i'm lucky--canoe country is at the top of the watershed for Hudson's Bay.i have been drinking out of the lakes for 25 or so years with no i'll effects.there are places where i filter water thru a Pur Hiker but thats to get out the heavy stuff like pollen or the tiny daphnia,water fleas, that are found close to shore.on the BWCA canoeing site this is a subject that is beat to death--filter,no filter,boil,chemicals,UV light...
closer to home,paddleing on the St Croix river i filter all my water. it's designated a "wild river" in the upper part that i make float trips on but with a village or farm here and there i don't trust the water quality.