Barry Shell answered on November 13, 2007, A:If you found this answer useful, please consider making a small donation to science.ca.
Plants and animals can live under ice because of water's unusual quality of being most dense at 4 degrees C. Ice has a density about 93% of water so it floats on top. Water is most dense at 4°C. Deeper water below the ice stays at 4°C because colder water rises to the top due to its lower density. So at the bottom of a frozen lake, stream or pond, it's always 4°C, warm enough for life-or hibernation at least. For more amazing facts about water check our water facts page on science.ca.