Grey water being dumped wasn't all just out in the woods but rather on campsites. It wasn't tree huggers in this part of the world that first complained of this practice. Our camp sites stank and we the campers complained and soil samples taken by the state/COE/counties environmental folks showed extremely high levels of the wrong type bacteria and other chemicals.
Our kids actually played in what ever the last campers had drained out on the campsite. Some less enlightened campers said they saw nothing wrong with watering campsite trees/grass/shrubs with grey water.....never thinking long term.
Animal poo in the woods isn't concentrated in one spot for years but scattered around the area they frequent nor do they dump harmful chemicals in the woods...... unlike humans.