Ecosystems are very sensitive to change. The living and non-living components of the ecosystem can be altered by either natural factors or human management.
Changes to the ecosystem caused by natural factors include:
drought
flood
fire
disease
Changes to the ecosystem caused by human management include:
introducing more fish (fish stocking)
altering the drainage of the land which may influence the amount of water
changing the pH level of the water
altering the nutrient levels of the water if fertilisers are leached into the water resulting in eutrophication