Preheat oven to 350°. In a large bowl, combine the cake mix, gelatin, eggs, oil and water; beat on low speed for 30 seconds. Beat on medium for 2 minutes. Stir in raspberries.
Pour into a greased 13x9-in. baking pan. Bake until a toothpick inserted in the center comes out clean, 35-40 minutes. Cool completely.
For frosting, in a large bowl, fold whipped topping into raspberries. Spread over cake. Refrigerate for 2 hours before serving. Store in the refrigerator. Garnish with fresh raspberries if desired.