I don't know if it's true, but I heard a private pond above Kushog, was stocked with pike by the owner, and it over flowed into Kushog (20 + years ago?). From Kushog, down Buckslide into Boshkung, up to Beech/ Maple etc., down to 12 Mile/ Mountain/ Horseshoe etc
Going from Balsam to Gull, there's 4 dams in between, I don't think that's how they colonized the upstream lakes.
Muskies were stocked in Brady, probably 40 years ago. They made their way down Anson Creek, which isn't much of a waterway, into Longford Township, Rainy, Big Trout, Logan etc. I'm pretty sure nobody thought they could get through there. The Longford guys were ticked off too.
Pretty amazing and scary too, how species can invade.