To ask the Secretary of State for Wales what are the causes of the increase between 1987 and 1988 in the percentage of rivers in Wales that fall into class 3 and 4 of the National Water Council grading system as shown in table 2.09 of the "Environmental Digest for Wales".

Between 1987 and 1988, 364 stretches of rivers in Wales, totalling 1,602.6 km, changed classification. Details are held by the Welsh region of the National Rivers Authority. The increases of stretches falling within classes 3 and 4, at 0.8 per cent. (37 km) and 0.2 per cent. (7 km) respectively are such that the authority does not consider them to be indicative of any significant overall trend.