River Characteristics

The characteristics of a river can change naturally without the influence of human activity or pollution. River characteristics can affect invertebrate populations without necessarily indicating the occurrence of organic pollution. When analyzing invertebrate data, keep in mind the effects of these river characteristics: Rivers tend to age or mature naturally as they flow toward the ocean from cold mountain headwaters and out across the warm prairies.

Rivers age and mature naturally

• Generally, the downstream sections of a river become warmer, slower, deeper, more nutrient-rich, more turbid and muddier. Some invertebrates prefer warm water.
  
  
• Downstream sections of a river are more likely to support organisms typical of fair or poor water quality.
  
  
• The type of river bottom (substrate) can affect the numbers and types of invertebrates. Rivers with muddy bottoms are more likely to support organisms typical of fair or poor water quality.

So, how do you tell if "older" rivers are polluted? That's a good question! The answer probably lies in evaluating a number of factors such as bacteria and surrounding land-use.