dredge, dredge up

When people dredge a harbour, river, or other area of water, they remove mud and unwanted material from the bottom with a special machine in order to make it deeper or to look for something.     

• Police have spent weeks dredging the lake but have not found his body. 

dredge up:

1. PHRASAL VERB

If someone dredges up a piece of information they learned a long time ago, or if they dredge up a distant memory, they manage to remember it.     

• an American trying to dredge up some French or German learned in high school.
  

2. PHRASAL VERB

If someone dredges up a damaging or upsetting fact about your past, they remind you of it or tell other people about it.     

• I wouldn't want to dredge up the past.     
• It's the media who keep dredging it up.

.... Cobuild