Talking of cleaning a, how thorough should one be? Even if you grow all your plants in baskets, it is inevitable that the base of the pond will, in a short time, receive a layer of mud and debris and probably small stones. In the case of liner pools the stones are worth removing for fear of damage. But a certain amount of mud is unavoidable and there is no point in continually removing it. Pond maintenance means preventing pollution above anything else. The decay and putrefaction of water plants and the from nearby trees, especially in a small shallow pond, can destroy the quality of the water and can prove fatal to fish. Any sign of an oily sheen on the surface of the water is evidence of some degree of pollution. Never allow the water to reach the stage you often see in dykes and ditches of becoming a smoky blueish colour. If it does the oxygen content is likely to be very low indeed and a very thorough cleaning-up operation is needed. But your pond should never reach that stage. An occasional clearing of dead leaves during the summer, a thinning of oxygenators from time to time, and a back of dead foliage in autumn is really all that is required to keep the pond healthy — a self-perpetuating eco-system. Some owners of concrete lower the water level from time to time to scrub the walls clean of algae — liners can be washed and rubbed down too — but I would only carry out this operation very occasionally, if at all. A certain amount of algae is always present. It can best be kept in check by underwater plants; but if blanket weed forms this should be removed by hand or twirled out on the end of a stick.