Question

The single largest threat against a river ecosystem is ___________.

a) pollution
b) silt
c) muttering
d) ransom
e) estuary

Answer 1

The obvious answer is Pollution. Hope this helped!

Answer 2

a) pollution

Step-by-step explanation:

Multiple environmental stressors, such as agricultural runoff, pollution and invasive species, threaten rivers that serve 80 percent of the world's population. These same stressors endanger the biodiversity of 65 percent of the world's river habitats putting thousands of aquatic wildlife species at risk.