This is most likely the result of increased run-off from the rivers, due to increased rainfall, which provided a greater abundance of nutrients and decreased predation from a dispersed fish population.
(This; is; most likely) (increased rainfall; provided; a greater abundance of nutrients) (increased rainfall; decreased; predation; from a dispersed fish population)
This increased rainfall increased rainfall
is provided decreased
most likely
a greater abundance of nutrients
predation from a dispersed fish population