This is not new. "The grapes in that ad are covered in vaseline! The milk is white glue!" And so on. People like pretty pictures. Maybe this news will spur a cleanup effort (spoiler: nope)
Well the reason there won't be a cleanup is that the lake exists for the power plant and the plant is still running, the US has similar water features near many of their power plants. According to the plant it's not poisonous per say, just not a good place to swim for irritant and safety reasons, and you don't want to drink the water. There are probably far more toxic naturally occurring areas than this based on the lack of immediate health impacts to visitors.