Environmental and Health Impact

• While the "Yuck Factor" for cleaning up after dogs might be obvious, the serious health risks and environmental impact are the real concerns. Dog waste often carries E.coli bacteria, viruses, and internal parasites, which are communicable and harmful to humans—especially to our children and the elderly.
• According to the Environmental Protection Agency (EPA), pet waste is a significant cause of non-point source pollution...
  "...for watersheds up to 20 square miles that drain into small coastal bays, two to three days of droppings from a population of about 100 dogs, can contribute enough bacteria and nutrients to temporarily close a bay to swimming and shellfishing."
• Contrary to some beliefs (or excuses), carnivorous animals such as dogs do not produce fertilizer for plants. Useable manure-fertilizer comes from herbivores (like cows and sheep) which, in turn, consume vegetation and return unused waste back to the soil to be taken up by plants.

source: http://bact.uwosh.edu/microlab/secondarypages/
beachwater.php0&w=381&sz=147&hl=en&start=10&usg=__UQc
_ftPO06BxpM5E4nHbqTw6l-Q=&tbnid=6CeUsX_jHfgfjM:
&tbnh=97&tbnw=123&prev=/images%3Fq%3Dclosed%2Bbeach
%2Be.coli%26gbv%3D2%26hl%3Den%26sa%3DG