Add blueberries, sugar, and water to a small pan and bring to a boil over medium heat. Stir and lower heat to a simmer for 10 minutes, mashing blueberries as they simmer.
Remove from heat and strain blueberry skins and seeds out of liquid, then allow to cool.
Divide blueberry syrup, rye, and lemon juice into 2 glasses over crushed ice. Top with sparkling water and stir before serving.