In time this overflows the low, east bank, flooding the washes. With prolonged rainfall or snowmelt, the Washes may become flooded from bank to bank. The biggest floods occur when high flow coincides with high Spring tides, and the Hundred Foot River can not carry away the fresh water. Powerlines in the direct route of migrating swans, or in between areas where they feed and roost, are a threat to the birds. WWT research indicates that flying accidents account for almost two thirds of deaths in Bewick's, Whoopers and mute swans.
Most collisions occur in foggy, misty or generally poor visibility conditions, or at dusk.
Many swans are electrocuted, as they span conductors on collision - this frequently leads to power interruptions. These were fitted with a helicopter which hovered above the line as two workers, suspended in a metal basket, attached the spheres. The work was completed in 1995 and since then, there has not been a single recorded swan death along the marked section. Journal of Avian Biology.