Skoghall mill is located on the shore of Lake Vänern. Lake Vänern is one of Europe's largest lakes with an area of 565 000 ha and a volume of 153 billion m3. The graph shows the TOC (Total Organic Carbon) level in Lake Vänern at its effluent point to the Göta River.
The water quality in the lake has significantly improved in the last 20-30 years. The improving trend since the 1970s is a result of instalments of waste water treatment plants for industries and municipalities, the closure of several industries, and improvements in agricultural practices. While reducing its discharges of oxygen-demanding substances to the lakes, the mills have increased their production of LPB significantly.
The mill at Frövi is located at a river near Lake Väringen, a shallow naturally nutrient-rich lake. The area is 18 000 ha with a volume of 59 million m3. The lake contains at least 16 different fish species.
The graph shows the outlet of BOD (Biological Oxygen Demand) to Lake Väringen from the mill in Frövi. The first reduction of BOD occurred due to an installation of biological aerated lagoon in 1972. A slight BOD increase followed an installation of Board Machine 5 in the beginning of the 1980s. It was successfully solved and BOD levels started to drop again after 1985. The water quality has considerably improved despite the significant production increase.