The electric blue waters of this pond in the Russian city of Novosibirsk has become the backdrop of many Instagram fans lately. Photographs of women in bikinis posing by the lakeside and visitors riding inflatable unicorns on the azure waters have gone viral on social networks. But authorities warn visitors not to be deceived by its appealing turquoise shade, because the lake is actually a toxic reservoir where chemical residue from a nearby power plant is dumped. The lovely color that reminds people of a tropical paradise is the result of a chemical reaction between dissolved calcium and metal oxides.