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What Effect Do Humans Have on the Freshwater Biome?

Humans have had an immense effect on the world's ecosystems since the beginning of the Industrial Revolution. While most of the environmentalist headlines are on the damage humans are causing to oceans and rainforests, freshwater biomes are perhaps in even greater danger due to human activities.

Dams
- Dams often harm freshwater habitats.
  
  Dams provide civilization with a great service. They re-route the flow of rivers, providing water for crop irrigation and a clean source of electricity for cities. This does not come without cost, however. Because dams reduce the area fish have access to, fish have far fewer options for breeding, which decreases biodiversity and overall fish population.
Agricultural and Industrial Runoff
- Agricultural and industrial pollution is severely harming the freshwater biome.
  
  One of the greatest threats humans pose to freshwater ecosystems is the sheer volume of pesticides and pollutants that they introduce into river systems. Increased agricultural and industrial runoff promotes the growth of algae in freshwater. This algae is a natural source of food for many species of fish, but it also consumes dissolved oxygen in the water. Runoff creates algal blooms so large that they deplete almost all of the oxygen in the area. This depletion of oxygen essentially suffocates fish and invertebrates in the area, creating a "dead zone."
Invasive Species
- Though direct human impact has had a great effect on freshwater biomes, other species of non-native animals can be even more devastating to these habitats. Often when an invasive species is introduced into a new habitat, it encounters plenty of food and no natural predators. This upsets the natural balance of the habitat, which allows these species to multiply and quickly choke out native species that now have to compete for food.
  
  Many species of Asian carp have been found in U.S. waters, which have proven to be voracious predators that can quickly deplete food sources. Zebra mussels are another invasive species in America which can multiply unabated, with their numbers climbing up to 700,000 mussels per square yard.
Drainage of Wetlands
- Wetlands are in danger of disappearing due to the need for crop irrigation.
  
  Few wetlands are left in the United States that are not protected by law; most of the wetlands were destroyed when they were drained for crop irrigation. Besides draining the water that fish species need to survive, wetland reduction also contributes to the decline of many other animals that feed on these fish.

Nature