Let the Urban Fishing Begin
Well the annual raising of the water in the Rideau Canal got under way over the weekend. Dow's Lake should be full by now, though past experience suggests it's best to give it about two weeks for all of the dead plant material (leave, etc.) to settle out and the bait fish and bugs to kick into gear. The Victoria Day weekend would probably be a good weekend to hit the backwater areas in the Arboretum for panfish and crappie.
The two week rule is also a good rule of thumb for the stretches of the Rideau River that have yet to be filled to summer levels as well. If you don't see or catch any panfish, perch, etc. it's a good chance the the bigger fish have yet to move into the shoreline structure.
The Jock R. on the other hand is looking better every day and is definitely a place to try if you're looking for walleye on the fly. Heavy buggers in the deeper holes work well.