The Manitowish River flows from the lake area southwest of Manitowish Waters (High Lake in Boulder Junction), through the Manitowish chain of lakes, westward to the Turtle-Flambeau Flowage in Iron County. The upper portion connects 25 lakes including the famous Manitowish Chain of Lakes.
The blue marker points out Boulder Junction. The red arrow points to Boulder Lake or High Lake. You can see the Manitowish River flowing under CH M just right of center.
I took this as some people in canoes floated under CH M.