dredge verb definition in Rivers and lakes topic from the Oxford Advanced Learner's Dictionary

dredge

 verb: Rivers and lakes topic
[transitive, intransitive] dredge (something) (for something) to remove mud, stones, etc. from the bottom of a river, canal, etc. using a boat or special machine, to make it deeper or to search for something They're dredging the harbour so that larger ships can use it. They dredge the bay for gravel.