Strange Mud:
Mariners reported an unexplained phenomena of suspended mud they notice off certain areas of the Coromandel Coast in India. It was more than just muddy water. It was as if the mud was suspended in the sea. The water went from clear to completely obscured. There was no foul smell to indicate that it was sewage. Local fish seemed to swimming about in it with no problem. Even in 1874 they had no idea as to what caused this strange occurrence.
Muddy Protection
Apparently these large tracts of peculiar mud were so smooth, that even during the height of a fierce monsoon, a vessel could run for shelter by sailing into the midst of one of them. Once the vessel was within this mud area, the water was calm compared to the surrounding sea (as if the ship was safely behind a breakwater). Maybe this suspended mud was some form of underwater mud volcano?
Reference:
Edinburgh Evening News, Saturday 19 December 1874, pg. 3.