Scottish Environment Protection Agency
Probably one of the best public sector sites: contains all sorts of up-to-date material, an education section, and interesting historical statistical data. Notwithstanding the cyber attack in December 2020, the site seems to be working well. The "Regulations" section is astonishingly detailed with reference and links to all of the relevant laws. There is also online access to SEPA's library. First class.
Scotland's Environment Web
This site brings together various public bodies with remits relevant to the environment. Not a lot of law, but a great resource for issues, mapping and data on Scotland's environment.
An enormous list of links to just about every environmental law issue and country. Last updated in 2013.
Friends of the Earth Scotland
Campaign group, contains a lot of information about the work of the campaigns and a limited amount of information about the legal issues.