Dredger

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A dredger was a worker who excavated sediment from the beds of rivers and similar bodies of water.

Dredgers mould "mud" into coal-like blocks. (TV: Thin Ice)

In 1814, Lord Sutcliffe used dredgers, hired and watched over by an overseer to collect the faeces of a serpent chained to the bed of the River Thames. This was moulded into blocks and sent to the steel mill, where it was capable of burning a thousand times hotter than coal. (TV: Thin Ice)

In 1894, dredgers saw a sudden increase in loose detritus in the Thames after a group of Gremlins settled upriver. (PROSE: The Curious Case of the Miniature Menaces)