OK, thought I'd step it up a bit and make the trivia a bit more challenging. Maybe it was too challenging.
ANSWER: 2.7 miles*
* from the San Francisco Fly Casting Club's printed "Brief History":
"...Since the Truckee River is designated as a navigable river, the Club asks that those floating the the 2.7 miles of river respect the fact that the waters as designated "Fly Fishing Only---Catch & Release" and respect the fact that shorelines are the private property of the Club for use by members and guests. The Club supports a number of fishing-related groups and respectfully requests that same support in return."