The figures have been gathered at the request of SEPA's board after its West Region expressed concern at the number of prosecutions being rejected by local Fiscals.
The data show that 302 cases were recommended for prosecution by SEPA in the four years from 1996/97. In 50 of these no decision had been notified by Fiscals - in some instances for offences dating back to 1997/98. Of the remaining 252 cases, 87 (34%) had been returned to SEPA marked "no proceedings".
Fiscals in several jurisdictions initiated prosecutions in only half or fewer of the cases referred to them by the Agency over the four years. They include Arbroath (17%), Dumfries (35%), Glasgow (50%), Kilmarnock (37%), Paisley (50%) and Stranraer (20%).
The problem has become particularly acute in the West Region. Of the 36 cases referred to Fiscals in 1999/2000, decisions have been taken in 31 cases - and in 20 (65%) of these the decision was not to prosecute.
SEPA declined to comment on the figures until its board has discussed them. But they are bound to reinforce its concern that the Scottish legal system is making it hard for the Agency to enforce the law. This summer, the board asked its solicitors to meet the Crown Office to discuss ways of raising the low level of fines generally imposed for pollution offences in Scotland.