What difference would it have made if ice were heavier than water.
Life in bodies of water would be unable to exist during cold periods. If ice were heavier than liquid water, it would sink to the bottom and a lake would freeze from the bottom up, killing most of the organisms. As it is, water reaches maximum density around 3.98 degrees Celsius. After that, as the temperature approaches zero, it expands becoming ice, which is less dense than liquid water. As a result, bodies of water, such as lakes, freeze at the surface. The less dense ice floats above the more dense liquid water. And, because this liquid water below the ice has a temperature of about 4 degrees which is greater than the freezing point, most life can survive during the cold winter months until the spring thaw.