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Fears that foam in the River Thames could be related to sewage works have been quashed by the Environment Agency.
Lumps of foam could be seen forming near Gravesend Town Pier today, and streaming down river, following similar reports in other parts of the Thames.
Waterman Mick Wenban said it had been an issue since the weekend.
"I saw it on Sunday," he said. "It seems to come up with the flood tide. I think it might be to do with sewage works.
"There was a lot at Shell Haven on Friday, so I took some photos. When I picked some up and rubbed it, it seemed to be slightly green, but no one seemed to know what it was.
"We were mooring up a gas tanker at Canvey Island and we all noticed this foam all over the river. There was quite a lot of it."
But the Environment Agency have since reported the foam is due to algae reacting to sunlight - and posed no health risk.
"It's algae," said Environment Agency spokesman Joe Giacomelli. "We've taken some samples of it and it's harmless.
"The foam forms as the algae breaks down. It's due to changes in water temperature and sunlight, and it's a naturally occurring event.
"We will see a lot of it along the coast and tidal rivers as the temperatures warm up."