There’s a lake full right in front of you!
Seriously, it’s a little work but if you boil lake water for at least 10 minutes and let it cool it’s safe for drinking.
Not a “this weekend” solution but if you’re a regular islander there are reverse osmosis filtration systems as well as filtration systems with UV light for sanitizing lake water. We’ve had a UV system that goes to a point of use faucet on the side of the kitchen sink for about 15 years, it beats lugging water jugs like we did before the filter.