Of the water on earth, about 2.75 percent is fresh water. Broken down further 2.05 percent is frozen in glaciers, 0.68 percent is beneath the ground as groundwater and 0.011 percent is on the surface in lakes and rivers.
Water has an amazing characteristic in that it breaks the norm of temperature densities. Most everything on earth gets more dense or heavier the cold it gets and less dense and lighter the warmer it gets. Water breaks this mold. As water gets colder, it does get more dense until it reaches about 39.16 degrees Fahrenheit. Once reaching and going below this temperature it then starts to become less dense. This is why ice floats on water.
This water density change has an important value to do with lakes. Depending on what climate a lake is in, this function of water causes a lake to mix from top to bottom. This is called lake turnover and it allows oxygen to reach all the way to the bottom of some lakes. Lakes in really warm climates don’t have turnover and carbon dioxide builds in the bottom reaches. In some rare occasions when temperatures have dropped in these areas, these lakes have turned over and sent all the carbon dioxide into the nearby land area in an event called a Limnic eruption. These deadly events have caused mass death like in villages around Lake Nyos, Africa. In most cases lake turnover is good. It redistributes nutrients and oxygen so fish can live at all levels. It allows them to survive being under the ice all winter.
Another important temperature related characteristic of water has to do with oxygen. The colder the water the more oxygen it can hold, and the warmer the water the less oxygen it can hold. This is an important determiner in what organisms can live within it. A healthy river has plenty of dissolved oxygen to sustain the aerobic organisms that live in and clean the water. In late summer when the temperature of water increases and it holds less oxygen, the warmer temperatures also increase the metabolic rate of fish and other organisms living there. This increase in metabolic rate causes the living creatures to use more oxygen than needed in cooler water temperatures. Oxygen levels can be further depleted by outside nitrates and phosphates and fertilizers reaching the water. Oxygen levels in water help keep it clean, so it’s important to have cold oxygen rich water for everyone- not just the fish.
This might be to much science for most of you, but to me it just equates that water is very special and needs to be protected.