In a medium saucepan, combine blueberries, sugar, and water.
Stir the mixture to combine the ingredients well.
Bring the mixture to a boil over medium-high heat.
Reduce the heat and let it simmer for about 10 minutes, stirring occasionally.
In a small bowl, mix cornstarch with 2 tablespoons of water until it forms a smooth paste.
Slowly add this paste to the simmering blueberries while stirring continuously.
Cook for another 1-2 minutes until the syrup thickens.
Stir in the lemon juice and mix well to enhance the flavor.
Turn off the heat and let the syrup cool for 5 minutes to further thicken.
For a smoother texture, blend the mixture in a blender until smooth.
You can also strain the syrup if you prefer a chunk-free consistency.