Hey, my first post, sorry to revive an old thread, but i felt the need to comment here. Im a kayak bass fisherman, in Ontario as well.
What the OP is talking about i believe is called starry stonewort. An invasive aqutic plant that is taking over some of the shallow areas here in southern Ontario. Ive noticed it especially bad in the holland river and lake Dalrymple. I have never been able to catch many fish in it, and i haven't seen or heard of anyone doing so either. It literally grows from the bottom to within a few inches of the surface and is so dense. It fills in the area like concrete. We call it “the carpet”. I have learned to just keep moving on from an area if i see it growing very thick or to go to the deeper weeds just off where it is growing, past the edge of it.
I have included pictures below off google of what it looks like.
(If the OP is talking about something different, my apologies).