There's a great article about how to catch Macks in this issue of Salmon/Trout/Steelheader and it references Lake Chelan.

You may want to throw in some Kokanee gear, too. This is their hot time and the best places are the same as the Macks, except a little shallower. Try the Monument area and the Narrows.

Good luck!
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Bless our troops.