Watermelon Sangria

Slice off the top third of the watermelon lengthwise (save for later use) and score fruit with a knife. Using a large spoon or ice cream scoop, scoop out watermelon and transfer to blender. Blend watermelon until smooth. (If desired, strain seeds.) Add white wine, rum, seltzer, and lime juice and stir until combined, then add limes and fruit. Refrigerate until chilled, about 2 hours, then serve.