Here’s the precise text taken from the DNR regs:
Chippewa River, Cornell Flowage, Old Abe Lake, Lake Wissota, and Chippewa
Falls Flowage (includes tributaries of the river from their mouths upstream to
the first dam or lake): There is no minimum length limit on walleye, but walleye
from 14″ through 18″ may not be kept, and only one fish over 18″ is allowed. The
minimum length limit on muskellunge is 40″ from Holcombe flowage upstream.
Motor trolling is permitted, but only up to the first road, bridge or railroad bridge.
Note that this starts with Chippewa River. So, if you’re leaving the big lake and heading upstream, no problem, you’re still in the Chippewa River….troll away! It does mean that you cannot troll once you go under the first bridge in an area like Stilson Creek or Paint creek, since these are tributaries to the lake or the river.