They are a major cause of erosion, flooding, landslides and silt-laden runoff, posing a danger to downhill communities and downstream fisheries.
(They; are; a major cause of erosion, flooding, landslides and silt-laden runoff, posing a danger to downhill communities and downstream fisheries)
They
are
a major cause of erosion, flooding, landslides and silt-laden runoff, posing a danger to downhill communities and downstream fisheries