Watermelon is safe for dogs. The high water and vitamin content of watermelon is good for them. However, dogs should not eat the seeds or the rind.
Watermelon seeds are potentially toxic to dogs if consumed in high quantities. A few seeds accidentally consumed by a large dog are not dangerous, but puppies and small dogs should avoid them entirely.
The rind may cause diarrhea and is a potential choking hazard. The pigments in the rind may cause a dog to pass green stool. This is not a sign of sickness, but it may be alarming,
It is always best to give a dog small amounts of watermelon at first to be certain that there are no adverse reactions.