Water quality in need of improvement, agency says

The quality of water in the nation's rivers, lakes and inland sea areas still needs substantial improvement, the Environment Agency said Tuesday.

The report released by the agency on its annual water quality research conducted nationwide in fiscal 1996 shows that water quality on the average achieves 73.7 percent of its required target. The total percentage has improved 1.6 points from the 1995 figure.

Substantial improvement of water quality is necessary for rivers and lakes, agency officials said. Rivers have achieved 73.6 percent of the required standard target, while lakes satisfy only 42 percent of the target.

Seawater areas have reached 81.1 percent of the target, the worst being Ise Bay in Mie Prefecture at 56 percent, followed by Tokyo Bay at 63 percent and the Seto Inland Sea at 78 percent. The calculations are based on biochemical oxygen demand and chemical oxygen demand indexes. While the BOD represents the water quality of rivers, the COD applies to lakes and seawater. Water quality deteriorates as the indexes increase.

The river with the worst water was the Benten in Kagawa Prefecture, showing 31 mg of BOD per liter. The purest water was found in the upper reaches of the Osaru River in Hokkaido, which had a BOD level of less than 0.5 mg per liter.

The lake that fared the worst was Lake Teganuma in Chiba Prefecture, with a COD level of 24 mg per liter, while Lake Kuttara in Hokkaido, with 0.7 mg per liter, ranked first on the list. Agency officials said improving the water quality of lakes is difficult once they become polluted. They stressed the need to restrict the use of chemical fertilizers that contaminate groundwater and control household waste water in urban areas, which are eventually released into rivers and seas.