When an iceberg falls into the lake, a layer of water can freeze to the underside. If this is rich in algae, it can form a green stripe. Brown, black and yellow lines are caused by sediment, picked up when the ice sheet grinds downhill towards the lake.
The water froze the instant the wave broke through the ice. That's what it is like in Lake Michigan where it is the coldest weather in decades. Water freezes the instant it comes in contact with the air.
