Dredging a lake takes around 2 weeks from start to finish depending on how big the lake is.
A small pond takes around a day or two to dredge once it's been drained down.
But a larger lake takes around 2 weeks after they drain the lake down of water to dredge it.
After dredging the lake the water is then returned to the lake and then rain water eventually fills the lake back up as well.
Dredging a lake removes sediments and other debris from the lake to keep the water in the lake healthy and clean.
The sediment or sedimentation is the natural process of sand and silt washing downstream and that gradually fills channels and harbors.
Some lakes may need dredged every 10 years and some lakes may only need dredged every 20 years or so.