It might not be easily seen in the picture, but it is a couple feet thick here as well. It has been suggested that golf courses or possibly a park along the harbour shore has been dumping their grass clippings into the water. I have been told that golf balls (I found one yesterday) and tees have been found in the muck, so one would have to guess that a near by golf course could be the culprit, but there is no real proof, just speculation. And it does seem like a lot of grass to be coming from one place.