 Freshets from Himalayan snowmelt created treacherous seasonal currents.But summer was better navigationally and the three gorges, described as an "150-mile passage which is like the narrow throat of an hourglass," posed hazardous threats of crosscurrents, whirlpools and eddies, creating significant challenges to steamship efforts.Furthermore, Chongqing is 700 – 800 feet above sea level, requiring powerful engines to make the upriver climb.