There are many factors that affect water temperature. For instance the color of the water, dark murky water will absorb more heat making it warmer while clear water will generally be cooler. How deep the water is also affects the temperature. Other variables are the amount of shade water receives, where the water is located worldwide, the time of the year, the temperature of the water supplying the waterway, and the amount of water. Most aquatic organisms are cold-blooded and therefore usually become more active in warmer water. Fish and other aquatic organism usually have their own optimum, or best, temperature. If the temperature varies too much from their optimum, they may have trouble surviving.