Heat oven to 425 degrees. Spray 8x8x2 pan with Pam. Drain blueberries; rinse and set aside. Stir together yogurt and egg whites in medium bowl; gradually stir in 1/2 cup water. Stir in muffin mix(dry) until moistened. Fold blueberries into batter. Spread in pan. Bake 23-27 minutes or until top is golden brown; cool. Mix powdered sugar and 2 teaspoons water in small bowl, using spoon. Drizzle over cake.