DNA can confirm the source(s). The Weirs beach has had this problem on an off for many decades. Waterfowl can certainly cause a problem. After this many days, I would have expected a constant source than birds or dogs. Have any particularly large families or RV's left the area recently?
Birds are a Huge source of contamination, particularly in areas where people feed them. Given that the beach had signs posted for two weeks with limited people, I would have suspected a nearby problem upstream.
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