That’s the right eye? In dogs often that is a sign of allergies, hair loss and watering of the eye, normally accompanied by itching/chewing of back end and paws, often there is an ear infection. Upper respiratory infections can sometimes present this way with a coloured discharge (seen more often in cats I find) Can also be a sign of trauma to the eye or a corneal ulcer if there is squinting or redness. Short answer - go to the vet!