But the results have only served to increase the fears of the small Alaskan village which spotted the colourful sight struck on their lagoon for the first time ever two weeks ago.
It soon disappeared but the local Eskimo community, which relies on the surrounding waters for its very existence, feared long-term damage to the water quality and particularly the fish and plants they use for food.
At first the leading theory suggested the goo was made up of millions of microscopic eggs.
But now scientists from the National Oceanic and Atmospheric Administration have confirmed the presence of fungal spores which create rust, explaining the luminous colour.
The gunk appeared August 3 at the edge of Kivalina, an Inupiat community of just 374 souls at the tip of a barrier reef on Alaska's northwest coast.
There was a report of dead minnows found in the lagoon the night the substance appeared.
City administrator Janet Mitchell said those fears would only intensify with the latest analysis, which did not include toxicity tests.
She herself was troubled about the community's dwindling reserves in village water tanks that will need to be topped off.
'We are going have more concern from the public,' she said. 'If I'm concerned, then there will be others with concerns.' Read More
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Douglas estimated the volume of the substance at more than a thousand gallons.
She said it was widely spread along the Wulik River and the lagoon, which is a half mile wide and six miles long.
Orangey water was reported as far away as the village of Buckland, 150 miles southeast of Kivalina.
She found no reassurance in the findings announced Thursday.
'The fact that they have not completely ID'd this thing still leaves more questions in my mind,' she said. 'I'm not comfortable with this thing.'