As Lake Powell drops, a waterfall forms at the reservoir’s upper end as the San Juan cuts down through sediments dropped when the reservoir was fuller. The resulting waterfall is a bit of an obstacle to fish:

The razorback sucker population estimate for 2017 alone was 755 individuals and, relative to recent population estimates ranging from ~2,000 to ~4,000 individuals, suggests that a substantial population exists seasonally downstream of this barrier. Barriers to fish movement in rivers above reservoirs are not unique; thus, the formation of this waterfall exemplifies how water development and hydrology can interact to cause unforeseen changes to a riverscape