Yes, swan poop can be as big as dog poop, but you will notice a lot of grass. If the swans are fed cracked corn and poultry layer pellets, the fecal matter will be more solid. If the birds only eat grass or other aquatic vegetation, then it can be semi solid to watery. More than likely, this is swan poop. The best way to find out is to clean the area, keep dogs away and see if the swans are actually pooping in the area. The Regal Swan