A very big lake indeed! The first requirement is a boat of some sort. (For me I mean.)
In June 1898 it must have been their own boat as I don't think the steamboats were up and running yet. I'll have a look in Yukon Archives and the MacBride Museum to see if I can get a hint of where to look. There really isn't much land access to the lake, and any markers were likely of wood so unlikely to have lasted.
I'll see what I can find.
Cheers
Carl