Actually, they are coming up to get oxygen.. but it looks cool!
(Lakes and streams breathe the same as living things. When they are covered with ice and snow they cannot get air and they much hold their breath until the ice thaws. While they are holding their breath the oxygen in the water is gradually used up by the living things sealed up in it -- fish, plants "bugs", snails, and hosts of microscopic life. If the ice lasts long enough, these living things die one after another as each kind reaches the point where it cannot stand any further oxygen starvation. Sometimes temporary relief is given by rains and melting snow that bring fresh, serated water under the ice, but no method of artificial respiration has been found that works. Sometimes, too, when water plants get enough sunlight through clear ice they produce small amounts of oxygen and delay the suffocation of the fish, etc.; but when snow and cloudy ice cuts off the light this does not happen. [www.total-fishing.com])