Many of the chemical, physical, and biological characteristics of a stream are directly affected by water temperature. Some species, such as trout, are quite sensitive to temperature changes. Water temperatures can fluctuate seasonally, daily, and even hourly.Human activities can adversely raise stream temperatures in a variety of ways. Thermal pollution can be caused by:* releasing warmed water into a stream from industry discharges or runoff from paved surfaces* removing riparian corridors, which increases solar heating* soil erosion, resulting in darker water, which can absorb more sunlightWater temperature impacts:* The amount of oxygen dissolved in water _ cool water holds more oxygen than warmwater* The rate of photosynthesis by algae and aquatic plants _ the rate of photosynthesisincreases with higher temperatures* The metabolic rates of aquatic animals, which increase with higher temperatures* The sensitivity of organisms to diseases, parasites, and toxic wastesHuman impacts are most critical during the summer, when low flows and higher temperatures can cause greater stress on aquatic life. It is important to note that the temperature of some streams are normally higher than others, depending on groundwater flow into the stream, weather, and other factors.