Fresh Blueberry Pie

1 9" pie shell (graham cracker)
4 Cups fresh blueberries
1 Cup sugar
3 T. Cornstarch
1/4 t. salt
1/4 Cup water
1 T. butter

Line pie shell with 2 Cups blueberries. Make sauce by cooking together 2 Cups blueberries and remaining ingredients except butter. Cook over medium heat until thickened. Remove from heat and add butter. When cool, pour over berries in shell. Serve with whipped cream.