Diverse land usage and water pollution by Michael Kelly , Joan Kadaras , Cyndi Knight , Melanie Hester . A network of streams and tributaries from the headwaters to the mouth of a river is called a river system. The land area that drains rain and snow melt to a river is called a watershed, each tributary to the river is part of a smaller watershed. Many watersheds have been altered as result of human needs for water, food, recreation, transportation, etc. Growing demands have led to pollution of streams and rivers.
Unwise land use further degrades water quality.
A river may be less healthy where it passes through farmland than where it passes through forested lands due to fertilizer runoff and sedimentation. As water flows through land being used for different purposes it picks up contaminants which change the quality of the water. Both additive and subtractive effects may be seen. The effect of urbanization on temperature of microclimates by Annette Sheffield , Karin Westerling . Urban environments differ from agricultural and wild lands in many respects.