Lake Vättern

Lake Vättern, Sweden's second largest lake (area 1,912sq.km/738sq.mi; 130km/80mi long, greatest width 30km/19mi) extends through the four provinces of Västergötland, Östergötland, Närke and Småland. Its water is so clear that the bottom can be seen at depths of up to 10m/33ft, and at these depths the surface appears green as a result of the reflection of light from the sandy bottom. The clarity of the water is due to the fact that the lake is fed partly by springs and partly by water from mountain streams, purified by passing over gravel.

The lake has an average depth of 40m/130ft, but reaches as much as 128m/420ft at the deepest spots round Visingsö. This great mass of water stores so much heat that the lake does not freeze until late in the year - rarely before New Year, and in many years not at all. On the other hand it is slow to warm up in summer. The colder water on the bottom supports a large fish population, including the Vättern salmon, a species of trout.