Use a knife and cutting board to cut the watermelon into smaller chunks, ensuring some seeds are included. Measure out 4 cups of the chopped watermelon.
Place the watermelon chunks into a blender and add 1/2 teaspoon of sea salt. Blend on high until the mixture is smooth and evenly combined, about 30 seconds.
Pour the blended watermelon mixture into popsicle molds, leaving a small gap at the top for expansion. Insert sticks and place the molds on a flat surface in the freezer.
Freeze the popsicles for at least 4 hours or until fully solid. The mixture should become firm, with visible seeds encased in ice.
Remove the popsicles from the molds by running warm water around the outside for a few seconds. Gently pull to release each frozen treat, showcasing the seed-studded icy texture.