01 - Combine cubed watermelon and fresh lime juice in a blender container. Blend on high speed until completely smooth and no chunks remain.
02 - Pour the blended mixture through a fine-mesh sieve into a clean pitcher, using a spoon to press the liquid through. This removes any pulp or seeds for a silkier texture.
03 - Divide the strained watermelon puree evenly among 4 tall glasses, filling each about one-third full.
04 - Place one generous scoop of vanilla ice cream into the center of each glass, allowing it to rest on top of the fruit puree.
05 - Slowly pour the chilled lemon-lime soda over the ice cream in each glass, pouring down the side to control the foam. Fill glasses almost to the top.
06 - Decorate each float with fresh mint leaves and small watermelon balls or thin slices placed on the rim of the glass.
07 - Serve immediately with a drinking straw and long spoon to enjoy both the liquid and ice cream together while still cold.