The conservation group says the increase in winterised cottages on and around Lake Saimaa is disrupting the seals' nesting. The endangered mammals are forced to move around during nesting season, resulting in higher pup mortality.
This year the WWF says the best area for seal nesting is around the eastern town of Savonlinna, where there is plenty of snow and ice. On southern Lake Saimaa, meanwhile, the snow and ice situation is poor from the seals' point of view.
WWF Finland calls the Saimaa seal "the most endangered seal species of the world". In the late 1970s, its population dipped to 150. Now that figure is up to about 270, with 63 pups born last year. Still, the group says a population of at least 400 is essential to protect the species from extinction.