Preheat an oven to 375 degrees F (190 degrees C). Grease a 9x9-inch baking dish.
Whisk the milk, oil, 1/3 cup sugar, and baking mix together in a bowl until no large lumps remain. Pour into the prepared baking dish. Whisk 2/3 cup sugar with the water in a clean bowl until mixed. Gently fold in the berries until evenly coated. Spread the berries over the baking mix batter.
