How do ice sheets form on creeks and streams?

They usually start from the edge, where there is something solid that is colder than freezing. Eventually exposure to cold air allows the whole surface to freeze over. It's a real battle between the cold sucking the energy out of the water at the surface, turning it solid, and the movemont of water bringing warmer water from below to the surface and carrying the cold water at the surface down where it can mix with warmer water. Eventually, though, if the air is too cold, the ice forms faster than the flow can prevent it, and once established, it thickens because the lower density keeps it afloat.

water is most dense at 4C which is like 35 F. That is just above freezing so when ice forms it floats to the top because it is less dense. Ice has 1/9 more volume than water.[Of course this means using the mass amount. the volume changes w/ a phase change]. Also u'll notice it'll form on a lake or pond before river because they arent as freeflowing.