Ice pack mostly solid. Ice has disappeared in the upper six miles of Lake Pepin but remains a formidable 17 inches at other points — more than barges can cut through even when pushed by 6,200-horsepower twin-screw pusher vessels. The latest borings by the Army Corps, on Wednesday, found blue ice, also called “black ice,” off Lake City and south to the Chippewa River delta. There remains no white ice on the 22-mile Mississippi shipping lane through lake. White ice is softer with air bubbles.