When Loch Leven in Perthshire got so covered in algae one day in June 1992 the event became known as “Scum Saturday”.
It was estimated to have cost the local community £1m in lost revenue from tourism.
Now a report by the NERC Centre for Ecology & Hydrology for Scottish Natural Heritage has shown that plants, fish and birds are thriving there. Numbers of Pochard, a diving duck, have increased from about 1,000 in 1990 to 2,400 in 2007.
The algal blooms were caused by excessive amounts of phosphorus entering the loch. However, steps were taken to clean it up.
These included Scottish Water upgrading the waste water treatment works in Kinross and Milnathort.