This means the spring floods that cleared the riverof vegetation no longer happen, making it difficult for the cranes to use the length of the river to roost out of range of most predators.
"This will help to make sure people can continue to enjoy the river ready for the start of this year's spring and summer boating season, " Mr Watts added.
Tests of female spring chinook from Dworshak National Fish Hatchery along Idaho's Clearwater River at Ahsahka likewise showed no evidence of the male-linked genetic marker.
Three Ukrainians were swept to death by the unusual flood last year when they were at a hot water spring along the Seti river some 20 kilometres north of Pokhara.
Continue along Pontocho, past the theatre where geisha perform public dances in autumn and spring, and you will come out near the river again and Sanjo Bridge, where much of young Kyoto is hastening towards a night on the town, or waiting for dates near the temple commemorating 39 noblewomen and children executed along the riverbank.