These are the gradings given by the Marine Conservation society in their Good Beach Guide 2008.
Recommended = MCS Recommended. Highest water quality standard & good treatment of any
continuous sewage discharges
Guideline = Good water quality standard only
Basic Pass = Passed EC Mandatory standard for water quality (statutory minimum)
Fail = Failed EC Mandatory standard for water quality (statutory failure)
A basic pass then for Nairn's two beaches. More on the BBC site about a general drop in standards around the uk: 'The MCS blamed the drop in water quality on an increase in storm pollution.'