Complex sentence: Now the river flows at a constant 46-47 ° F year-round, because the water is released into the river from the lower regions of the lake, where the water's high thermal mass keeps it at a constant temperature.
Split into simpler sentences: Now the river flows at a constant 46-47 degrees (F) year-round. This is due to the fact that water released into the river is released from the lower regions of the lake, where the water's high thermal mass keeps it at a constant temperature.