From Jackson Lake downstream the river remains within a pristine ecosystem with the exception of its flow-regime, which is altered by the operation of Jackson Lake.
(the river; remains; within a pristine ecosystem with the exception of its flow-regime) (its flow-regime; is altered; by the operation of Jackson Lake)
the river its flow-regime
remains is altered
within a pristine ecosystem with the exception of its flow-regime
by the operation of Jackson Lake