In a blender, combine watermelon, lime juice, agave, and chili powder. Blend until smooth.
Pour watermelon mixture into 3 oz. ice pop molds and place cover on mold. Insert popsicle sticks and freeze solid for at least 6 hours or overnight.
To remove ice pops from molds, briefly dip molds in cool water just long enough to get ice pops to release. Place on a baking sheet and return to freezer for 10 minutes.
Serve with chile-lime salt. Leftover ice pops may be kept in the freezer in a plastic freezer bag or container.