Answer:
A dredge can be a machine like a bulldozer that scoops out dirt and sand from the bottom of a harbor to make it deeper and safer for ships. They need to get a new dredge because that one isn't digging deep enough.
As a verb, to dredge is the act of doing that. We will dredge the harbor next week, so prepare for traffic problems.
You an also "dredge the bottom" figuratively to "dig up dirt" or unkind facts about someone. He dredged up the fact that I'd been married before.
And you can say something like "I dredged up an old photo that showed Rita in a wet t-shirt contest."