Place watermelon flesh in a large high-speed blender then pulse until a liquid forms then keep blending for another 30 seconds to 1 minute (you may need to do this in batches depending on how big your blender is).

Using a fine mesh strainer or cheesecloth, strain juice into a large pitcher (again, you may need to do this in batches). Mix in the lime juice and simple syrup. Enjoy plain or make watermelon margs below!