Large Silverstripe

Actually this butterfly had fallen into the lake and we spotted it
struggling by the edge of the lake. First I managed to take a couple of photos, and then tried to rescue it from the soggy area, and the drizzle, but it was flapping so much it was hurting itself. With a heavy heart therefore, we had to leave it there. We saw it dead the following day. The powdery substance mainly on its right wing is rhododendron pollens fallen into the lake. This year there was an explosion of Rhododendron campylocarpum blooms, as a result many areas in the lake were covered with this white powdery pollen.
Do these butterflies get carried by wind or come flying all the way to this cold place from the lower reaches - along the same river - where I'd spotted and posted a month ago! We saw a healthy one flying in the morning sun. We, father-son were happy!