A black dog with a blue collar is jumping into the water.
A black dog wearing a blue collar is chasing something into the water.
The dog is jumping into the water, there is no information given about why or what else is near.  It can't be assumed the dog is chasing something.
Just because a dog jumps into the water does not mean that he is chasing something.
Just because a black dog with a blue collar is jumping into the water does not mean the dog is chasing something. Not all dogs are back.