Add fresh blueberries, lemon juice, and ice to your blender.
Secure the lid tightly and blend on high speed until the mixture is smooth and icy, about 30-40 seconds. You should see a vibrant purple slush with tiny frozen bits.
Stop the blender and check the consistency; if it's too thick, add a splash more lemon juice or a little water and blend again briefly.
Pour the blueberry slushie into chilled glasses, and notice the bright, icy appearance combined with flecks of deep purple.
Garnish with fresh blueberries or a lemon wedge if desired for an inviting presentation.
Serve immediately with a straw for a cooling, refreshing treat.