Fished my local river Rye in N. Yorkshire after work this evening and was greeted by a sad sight

. There was a fly hanging from a branch over the water with about 18 inches of loose line. Hooked in the mouth and dangling above the water was a very dead bat

It wasn't there last time I fished a couple of weeks ago and the water has been higher than it is now, so maybe the angler who lost the fly couldn't get to it - I only just reached it with my hand after wading to within a couple of inches of my chest wader tops. A few months ago I found another fly in almost the same place dangling from a branch and I waded to it to get it.
Years ago I read in (I think) Trout and Salmon Magazine about bats being caught on lost flies and have always made sure that I retrieve every fly that I possibly can (whether mine or someone else's) either by wading to them or using the rod tip to hook them out.
Please be aware that bats are very easily fooled by a dangling fly and I know that ducklings will also take fishing flies if they are close enough to the water surface, so if it is at all possible don't leave flies behind.
BTW the bat was caught on a barbless fly but had not managed to escape.
Keith