The clues to solving this bonus cache can be found in both of the other two 'Back in a Flash' caches on Mohr Island.
You will need water transportation to reach the cache, about the size of a pill bottle, which is NOT reachable from your watercraft. There is a handy place to beach your craft though. Motorized boats may find it tricky to navigate close to the final, but it is possible. The beaches are firm enough to walk in from any motor craft
This cache will take you to a put-in on Dunrobin Road, just west of Ottawa, where you'll find parking at the end of the road, and a launch for your cartop boat.
FREE canoe and kayak launch and parking at the additional WP on GC596K5.