Watermelon is fine for dogs. Remove the seeds and rind, give them the flesh, and most dogs will go absolutely crazy for it — especially cold, on a hot day. My golden retriever loses his mind when I pull one out of the fridge in July.
The flesh is 92% water, low in calories, and has some decent nutrients — vitamins A, B6, and C, plus a little potassium. It's one of the better summer treats you can offer, honestly.
Two things to remove first
Seeds: Black seeds should come out before you hand anything over. A couple accidentally swallowed won't hurt, but in larger quantities they can cause digestive trouble. If you regularly feed watermelon, just buy seedless — saves time.
The rind: Leave this out entirely. The hard outer skin and even the lighter green inner rind are tough to digest and can cause intestinal blockage. Stick to the red flesh. That's the part dogs actually want anyway.
How much is too much?
The usual guideline for treats is that they shouldn't make up more than 10% of a dog's daily caloric intake. Watermelon is low-calorie enough that this isn't a strict concern, but that doesn't mean feeding them half a watermelon in one sitting. A few chunks for a medium to large dog, maybe more for a big one, and you're in good territory.
Too much of any fruit can cause loose stools — not because of toxicity, just because of the fiber and natural sugars hitting a digestive system that isn't used to it.
A genuinely good treat option
Compared to a lot of store-bought dog treats, watermelon is pretty good. High water content means it helps with hydration, it's low in sugar relative to other fruits, and most dogs find it exciting. If you want something similar that travels a bit better, blueberries are another solid option — easy to portion and nutritionally decent.
Unlike grapes, which are a hard no for dogs, or even bananas (which are fine but higher in sugar), watermelon is about as low-risk a fruit treat as you can give a dog. Remove the seeds and rind and you're good to go.