I know nothing of this property, but would suspect that it was originally one single parcel of Patent Land from the mid 1700's to late 1800's. If there isn't a navigable river in or out, then the lake bed is also part of the parcel. Water may very well be included as part of the patent as well.. similar to the marsh off of Scugog. If that is the case, I would be tresspassing if I landed on said lake...but that's dicey.. as if I take off before I'm charged I just made the water surface an aerodrome and the province has no constitutional capacity to access planning power over an aerodrome, so they would have to charge me in federal court to get anywhere.
Since the property surrounding the lake is privately held with no municipally owned allowances or easements then it is what it is.. private. I presume the original land owner applied for and was granted a plan of subdivision and was given same without the municipality asking for a "green space" or assuming the roads. Considering what many old Crown land patent transfers have written in them the township really had no jurisdiction over anything the developer did anyhow.
To skip all the someone take the time to find out what the original parcel of lands registration # is and what municipality it was in when the patent was granted a hundred or two years ago. Submit the info to the MNR in Peterborough and blow the $32 ($50 for a certified copy) and find out what the real deal is. Oh.. the current wait to get a copy of a Crown land Patent is 6 to 8 months... as I'm waiting for mine.
Launch from the guys yard that is giving you permission.