Most clean up dives - Little Lake, Peterborough; and Campbellford - are normally scheduled later in Aug/Sept. so that the boating season's "droppings" can be dealt with.
You will also be competing in June/July/Aug with prime diving dates that many divers have already committed to other events.
I would happily attend. You might want to put in a call to the Adventure Divers shop in Peterborough or whomever handles the Campbellford dive for some logistical tips.
Why not blend garbage recover with enviro dive as they do in Peterborough (eg. installing fish habitats, etc.)
Consider segregating certain areas for newer divers and monitoring entry/egress depending on how silty the site is.
If heavy objects are being recovered, make sure it is divers equipped and trained to do so...
Marmora for the non-Ontarians is a delightful hamlet, less than an hour's drive East on Hwy 7 from the Metropolis of Peterborough (Peterborough? The place where Toronto vacations, slightly NE of GTA...)