Beat the whip until soft peaks form. Spread a half to two-thirds of it into the bottom of the graham cracker pie crust.

Combine one cup of the blueberries, water, sugar, and cornstarch in a small saucepan and cook over medium heat until the mixture is thickened and bubbling. Remove the pan from the fire and stir in the lemon juice and margarine until combined. Scrape the mixture into a bowl and cool to room temperature.

When the mixture is cool, stir in the remaining cup of fresh blueberries. Pour the blueberry mixture into the lined crust. Decorate the top of the pie with the remaining whipped cream or reserve the cream for another use. Refrigerate until chilled.