Abstract
On small islands in Okinawa, surface drainage from farmlands is stored for agricultural usage in storage ponds constructed along the ends of watersheds due to the lack of large water resources. Water from farmlands contains much fertilizer and algae pollution. In such areas, although drop irrigation systems have been adopted, they are not useful because the pipes choked with algae. Algae growth depends on temperature, nutrition and light. Therefore, removal of such elements prevents water from being polluted by algae. The authors, therefore, tried to block the light by covering the water surface with sheets in order to prevents the algae growth in the ponds. The result was that this method was recognized as an efficient method of prevents the algae growth in the ponds.
