Volunteers in Bosnia placed a Christmas tree at the bottom of the lake in the Hutovo Blato Nature Reserve.
They say the stunt is aimed at drawing attention to the reserve, which has suffered after budget cuts.
The tree and decorations will be collected after the new year so there is no adverse effect on the environment.
Around 250 people dressed as Father Frost, the Slavic version of Santa Claus, ran through the streets of Kiev, Ukraine, as part of a charity Happy New Year run.
Event organizers say the money raised will go to orphanages for disabled children.
More than 100 cats took part in an international cat pageant on Saturday in Israel.
Cats of all shapes and sizes from about 100 different breeds competed for prizes in different categories.
The event also featured the selection of the "king" and "queen" of the cats, who will represent Israel in future international cat competitions.