Hi Sorry I haven't been able to reply to this earlier.
Two things have happened, yes a certain amount of water runs down from the hills and reaches the sea... and it is indeed green, which is probably some sort of residue from the forest... and I'm sure this followed a heavy bout of rainfall... and it undoubtedly happens every year.
However on about the 2nd or 3rd of July one of the tractors / jcb's appeared and started removing sand from the beach. He took the sand from in front of Pelangi right up to the last resort before the beach turns around the corner (I think it was Redang Bay). The Tractor took a section of the beach about 3 metres wide, about 1 metre deep and about 100 metres long. Each time he took a load of sand he then drove the tractor either around the beach and towards Laguna or in between the some of the other resorts (Bay, Pelangi Ayu Mayang). Naturally I couldn't understand what was happening to the beach and why he was doing it.
We went to bed and returned the next morning and there it was. A massive trench right in the middle of the beach! I spoke to some of the guys in Coral and they hadn't a clue what was happening... nor did anyone down at Redang Holiday Villa!
I can imagine that the water from the hills generally runs right into the sea, but now the water runs from the hills, fills this trench and gradually runs out to sea!
I'm afraid I don't have any photos as I can't scan my print outs... and I can't imagine this removal of sand was the benefit of the marine life!!!
If anyone does get to the bottom of it I'd be extremely interested to find out what was happening!