I have a cabin outside of Cumberland (12 miles from Turtle Lake). Big Sand (350 acrues) and Little Sand (150 acres?) have muskies. I don’t know that either would be considered ‘good’ muskie lakes. I’ve heard good things about Rice Lake (about 20 miles from Turtle Lake) for numbers but haven’t fished it. Bone Lake is another good choice. Shell Lake has muskies but is about 25 miles from Turtle Lake. I also think they fish them in the Apple River outside of Amery. These are the lakes I am familiar with in the area. Good luck.
The Apple River Flowage in Amery is LOADED with muskies, there are some nice ones, but most are in the lower 30’s…if you are looking for numbers of BIG fish, your best bet would probably be Bone Lake, just northwest of Turtle Lake.
Deer Lake is west of Turtle lk on n side of hwy 8. Handy to get to and fairly productive. Bone has quite a reputation and decent launch on north end. Decent action around north end, much good structure throughout lake. Sand (Cumberland) can be very good, but launch needed repair my last time out, caution. Big Round (by the res)also has muskiy but not in the numbers it used to. Good Luck.