What was the role of a dredgerman?

"There are many types of dregermen but they all do a similar type of job ranging from operating a boat mounted crane with a bucket scooping mud stones etc. from rivers & canals, to a coal dredgerman who recovers coal dropped into the water whilst loading at staithes. The coal dredgerman would operate from a rowing boat using a perforated scoop, they where also usually employed part time sweeping the coal & coal dust into heaps on the quay.

A gravel dredger often works a machine with a line or belt of buckets powered by a stem engine.

A stone dredger at a quarry sorts the inferior stone from the bettemessage=There are mainy types of dregermen but they all do a similar type of job ranging from operating a boat mounted crane with a bucket scooping mud stones etc. from rivers & canals, to a coal dredgerman who recovers coal dropped into the water whilst loading at staithes. The coal dredgerman would operate from a rowing boat using a perforated scoop, they where also usually employed part time sweeping the coal & coal dust into heaps on the quay.

A gravel dredger often works a machine with a line or belt of buckets powered by a stem engine.

A stone dredger at a quarry sorts the inferior stone from the better."

http://www.british-genealogy.com/forums/archive/index.php/t-6312.html

DREDGERMAN Oyster fisherman

DREDGERMAN On the Thames, collected debris from other vessels which had fallen in the river

http://shadowsoftime.co.nz/definitions2.html

A long, but well respected, novel of Charles Dickens opens with two dredgermen who makes a gruesome discovery in the river Thames:

"Our Mutual Friend" begins with Lizzie and her father Gaffer Hexam patrolling the river in the dark of night. Pulling a body out of the river for the potential reward money, the novel jumps right into the action with a bang. The body is presumed to be that of young John Harmon, just returned from South Africa to claim a huge inheritance from his recently deceased, hateful and miserly father.

https://en.wikipedia.org/wiki/Our_Mutual_Friend