MECHANICAL HARVESTERS used in California
Mechanical harvesting machines are used in rivers and lakes. They are equipped with cutter bars that cut submersed plants from 3 to 6 feet below the water's surface. The material is usually collected and removed from the lake or river. Another type of mechanical harvesting device is a dragline. Draglines are usually chains or cables connected between tractors on either side of an irrigation canal. As the line drags along the canal bottom it uproots aquatic weeds which are collected downstream. Collection is usually by manual labor at the next trash rack downstream from the dragline operation.
Mechanical harvesters usually remove filamentous algae as well as submersed plants. There are no use restrictions on the water during or following harvesting operations. The harvested material is removed from the lake reducing the likelihood of oxygen depletion problems and nutrient release by decaying plants. Harvesters can be used to cut lanes from boat docks to open water or around swimming areas.
Harvesting is similar to mowing a lawn and repeated harvests may be required. Mechanical harvesters produce many plant fragments which are not collected, and it may enhance spread of the weedy plant throughout the lake. Many small fish and invertebrates which live on or around the harvested plants may be trapped and removed from the lake.