The Directive sets standards for chemical and physical parameters which are intended to maintain water quality suitable for cyprinid or salmonid fish. A total of 34,255 kilometres of fresh waters - more than 70% of mainland Scotland's rivers - have been designated under the Directive since 1982.
The new designations add a further 2,300 kilometres to the list. All of them have been designated as salmonid waters.
Not all of the previously designated lengths comply with the Directive. According to Mr Lang, the latest monitoring results showed that 33,523 of the 34,255 kilometres designated in 1989 met the EC requirements.