In a medium-size saucepan on medium-low heat, stir blueberries and sugar together and allow the berries to cook down and start releasing their juices, about 5 minutes. Stir frequently. Once blueberries have released lots of liquid, mash them down and cook for another 5 minutes. Mash one last time and then strain blueberry syrup into a large measuring cup and set aside to cool down completely.
Squeeze all of your lemons into a large measuring cup or bowl. You should wind up with about 2 cups of lemon juice. Straining your lemon juice is optional but I like to get all of the pulp out. Pour lemon juice and water into a large pitcher along with blueberry syrup and stir.
In a small saucepan, whisk sugar and water together until all sugar is dissolved. Gradually add the simple syrup to your blueberry lemonade until it is sweetened to your liking. I use abut ½-3/4 cup to sweeten mine. Serve over ice with additional blueberries for garnish.