The mysterious blobs washing up on Fiesta Island are dead sea sponges, a city consultant has found. They are not congealed blobs of sewage or septic tank innards as previously believed.

So why do they stink?

The consultant, Keith Merkel, writes in a letter released this afternoon:

[T]he strong odor from the material is a result of the organic decay of the dead organism and anaerobic bacterial degradation of the material.

Translation: It’s rotting.

Merkel said the sponge naturally occurs in Mission Bay’s warm waters. It’s commonly found during surveys of the bay’s bottom, he said. But it is rare to find it washing up on the beach.

Merkel writes:

[W]hen live, it naturally sinks when returned to the water. For this reason, it is of greater interest to consider why the sponge is dying in such numbers and washing ashore, a phenomenon that I have not seen before in over 20 years working in Southern California bays and most particularly Mission Bay.

City Chief Operating Officer Jay Goldstone said in a memo that the county will continue monitoring bacteria levels and within two days could downgrade the water closure to an advisory.


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