Left to their own devices, rivers change constantly. Snaking side-to-side across floodplains over ages, they eat the land away and deposit it elsewhere. Both beavers and fish are all too familiar with their fickleness and power.
Some will eat, some will spawn, many will die. So long as the perennial springs in Arctic Refuge keep flowing and the sea keeps giving and taking, this cycle will continue as it has for thousands of years.