清淤

qīngyū
to dredge; to remove sludge

CEDICT

to remove silt (in rivers, lakes and water channels)

Wiktionary

清除水體（河、湖等）底部的淤泥

維基詞典

Entry Composition

1 清 qīng
  1. (of water etc) clear; clean
  2. quiet; still
  3. pure; uncorrupted
  4. clear; distinct
  5. to clear; to settle (accounts)
2 淤 yū
  1. silt
  2. river sludge
  3. to silt up
  4. choked with silt
  5. variant of 瘀 yū