To make blueberry simple syrup: Combine sugar and water in a medium saucepan over medium - high heat, stirring until the sugar has dissolved.
Stir in blueberries and bring to a boil; reduce heat to low and simmer until blueberries have broken down, about 5 minutes. Strain thorough a fine mesh strainer, into large pitcher. Cool to room temperature.
To make fresh blueberry lemonade: Into the pitcher with the blueberry simple syrup, stir in the lemon juice and water. Place in the refrigerator until chilled.
Serve over ice and garnish with a few frozen blueberries in each glass and a lemon slice.