Human Impact Humans can alter natural temperature characteristics of a stream by direct actions to the waterway or indirectly through alterations to the watershed. When industries and community water authorities withdraw water from a stream, it may decrease the water depth. Since shallower water heats up more readily than deeper water, water withdrawal may increase stream temperatures. Water released from dammed lakes can also alter temperatures because it is often withdrawn from near the lake bottom and is often cooler than the stream temperature in the summer, warmer in the winter. The shock of these rapid temperature changes can be too much for aquatic life to handle.
Humans can alter the land use around a waterway and affect the water temperature.
Removing the streamside forests for farming or during timbering eliminates the shade provided to the stream. Sunlight is no longer blocked. The removal of streamside forests and any other actions that promote soil erosion also increase the water temperature as more heat soaking sediment enters the stream. Urbanization is another heat causing pollution source. Rainwater that flows over hot paved surfaces warms up and eventually enters the stream.