Yes. Watermelon can have a mild diuretic effect, which means it may make you pee a little more than usual. This is mostly because watermelon contains a lot of water, so eating it adds extra fluid to your body.
This does not mean watermelon works like a diuretic medication. It should not be used to treat swelling, high blood pressure, kidney problems, or fluid retention.
For most people, watermelon is simply a hydrating fruit that may slightly increase urination. If you are peeing much more than usual, have swelling, pain, or reduced urination, it is best to speak with a doctor.