If neglected, ponds, lakes and lagoons can become stagnant, full of algae/scum and emit putrid odours. In some cases, the lack of oxygen kills off natural eco systems which exacerbate the problem. Traditionally, ponds have been dredged, treated with chemicals / enzymes and in some cases, concrete lined. These methods are very expensive and generally do not work due to the anaerobic nature of the environment. The use of chemicals is very expensive, requires specialist/protective application, kills the natural environment and usually requires the sludge to be disposed of by road transport.