Truffle, I have owned dogs for thirty years, During that period the problem of dog poo has become a serious problem, as you rightly say.
While other posters who describe the socially aware way to clean up after one's dog are right, the problem remains of dealing with refuse in general and excrement in particular. The country's rivers are not coping.
The popularity of dog ownership means that dog poo makes the disposal problem a lot worse, and this has increased during the past thirty years.
Dog ownership must be viewed as a luxury not as a right. Dog ownership adds a great deal to any individual's ecological footprint.