Mystery over deformed whitefish continues

Up to 40% of male whitefish were deformed Keystone

The fish population of Lake Thun in the Bernese Oberland appears to have recovered over the past few years, after widespread deformities of their reproductive organs were detected, beginning in 2000.

Bern cantonal authorities say a new study found that the number of male whitefish with deformed reproductive organs have dwindled.

The phenomenon which caught international attention was linked to plankton the fish fed on but the reason for the abnormalities was never established scientifically, despite numerous investigations.

Environmental experts have not ruled out the possibility that chemicals used for the construction of a major alpine tunnel 15km south of the lake may have had an impact. The rail link opened in 2007 for traffic.

Initially it was feared that the abnormalities were caused by chemicals from thousands of tons of army munitions dumped in the lake between the 1940s and 1963.

A regular monitoring of the water quality will be continued according to a statement published on Wednesday.

Up to 40% of all male whitefish caught by fishermen between 2001 and 2009 showed changes in their reproductive organs.