The 1650W is an older unit. It was available in 2 models, one used Navionics cartography and the other used C-Map (Jeppesen). Since you have a card for Lake Ontario you know which format your 1650 takes.
Navionics no longer supports the format these machines used, Jeppesen/C-Map does.
You will have to check with those vendors to see if they produced charts for the Finger Lakes. If your unit is Navionics you might check on E-Bay or various forums to see if there is someone selling a used card. If it is C-Map you should be able to buy one if they have coverage for your area.