It would depend on there already being beach landing craft in the lake when the ...

It would depend on there already being beach landing craft in the lake when the encirclement happened. There weren't any other major ports on the lake at the time other than Leningrad and Shlisselburg which the was on the German side of the front and heavily contested. The German line also went to the Southern bank of the River there up until it turned North West to get into the city so you couldn't use that so the options for bringing food in via the lake were pretty limited and any losses would be effectively permanent until the siege was broken.