Michael Anderson uses a long bit on a drill to bust through the ice on Silver Lake in Eagle River. “That would be a good depth for an ice castle right now,” Anderson says, measuring about 15 inches of ice. That’s plenty for harvesting and forming into blocks for ice-castle building. But there’s a problem. A deep layer of slush on Silver Lake makes it inaccessible to the machines and trucks needed to transport ice blocks. Without the ice blocks, there’s no ice castle downtown, and that means