Topography affects water temperature in a variety of ways. Primarily, and most obviously is the aspect that differing geological formations cause different parts of the water body to receive more or less sunlight than others. This may be due to several factors that cause some areas of the river to heat, while others do not. Forest cover is one big determinant of this, while the area of water being observed is another. In bodies such as rivers that may span great distances, the closer the river comes to the equator, the more the temperature tends to rise. Furthermore, as its distance from the equator increases, the opposite is true.
Another topographical issue that may change the water temperature is the location of the entire water body. In the event the water source is in a valley (most common), much of the rain that falls over the valley will flow into the water and cool it. However, if the water lies atop a hill or on flat grounds, most likely the temperature will not be affected so drastically by rainfall.
A final aspect on how topography can affect water temperature is the distance to the nearest industry. For example, many factories and production plants produce thermal pollution which can significantly raise the temperature of neighboring waters. This usually heats the water to unsafe levels creating a environment which supports little or no life. Furthermore, the water quality in these areas is usually very poor.
Topography has a strong impact on water temperature which is an important part to all water quality.