I talked to a DNR guy who told me there is an emerging line of thought that the e. coli found in these beach monitoring programs is actually a self-sustaining phenomenon. That it actually grows in the wet sand.
That is not to excuse human pollution, which is obviously occurring as well. But, much of this may be a natural ecological issue, from geese and wildlife, and then the resulting bacteria adapting to grow well in a beach environment.
This might explain what's going on at a lake beach here in South Minneapolis. 40 years ago it was crowded with neighborhood kids. Today it might as well be paved over.