If rivers and ponds have currents, why do they freeze with a flat surface?

Question

i.e. the Yukon River--some passes freeze solid enough to cross ice safely but the current is especially strong.

Answer 1

when the water freezes, it freezes from the outside in. So it all starts to freeze slowly, and the ice runs into other ice and builds up on the top; meanwhile, the current stays strong under the surface.

As it stays cold, the ice gets thicker and thicker on top and the current is kept under.

Answer 2

The question itself isn't correct completely: As the surface of a current, i.e. the waves, also is a result of the wind with enough strong wind combined with strong freezing the ice may not be flat. Even little wave-like ribbles may be found sometimes.

Answer 3

rivers don't freeze. the surface area freezes but the flow is still strong under the ice. one small area freezes then more water attaches itself as it freezes giving it that flat look. ponds don't have currents.

Answer 4

the surface area freezes and sometimes it's cold enough to freeze even further down. But the current remains, just under that crust of ice.

Answer 5

Water, as with most materials...

when it freezes the molecules tend to align themselves in compact crystaline formations.

The surface is not perfectly flat... or else a zambone would never have to be used... but it should be in a rectangular matrix look.

Answer 6

The surface is solid an so it is not affected by the current of the liquid\water below.