After the plants and grass from the ditch side have been mowed, the (small) ditches are manually cleared of sludge and dirt that impedes the water flow. The tool also serves to dredge ponds and other water features.
The cleaning of the ditches is done at low tide, after a period of drought. One starts at the lowest point and against the current.
More technical information on the dutch version of this tool page.
See also the drag-net. [MOT]