My puppy is 6 months old and I just noticed green discharge from his left eye. Any idea of what it may be caused by or if this needs vet treatment?

I don't know if it is the same for cats and dogs but when My kitten was 3 or 4 months old he had a green discharge coming from his eye. Just so happened that he had to get shots on the day I noticed it and the vet said he had a cold gave me some antibiotics and that cleared it up in a week. I say take the puppy to the vet.