A word of warning, this post may not quite equate to the experience of wildebeest crossing the Mara river or seeing the migration of salmon being fed on by bears and wolves on the west coast of Canada and Alaska.  No, this is a thoroughly British mini and very discrete event - more of a curiosity. 

There is a small stream (about 4 to 6 feet wide) that flows into a small lake / very big pond (52 acres) near where I live.  It’s part my regular dog walking route.  Yesterday, about 50m from where the stream joins the lake I noticed some unusual moving shadows in the water.  As I looked through the rippled surface I could make out fish in the water.  Now, it’s not unusual to see fish.  There are often a few small fry and sometimes fish up to about 6” or 9” long to be spotted in the stream.  This time there were thousands (with no exaggeration) of small fish all no longer than 3”.  This spot is just below a tiny baffled weir in what on a larger river might be described as a weir pool.  It was this little barrier that was holding back the fish.   The fish filled the stream for a distance of about 25 yards.  

This behaviour is quite strange.  There isn’t much to migrate to up this stream and October certainly isn’t spawning time for coarse fish.  Perhaps they are congregating to escape predation in the pond by using this quiet backwater.  I recall seeing these groupings here in at least two previous years but not on this scale.  

Anyway, I returned a bit later with a camera and, most importantly, a polarising filter to cut out most of the surface reflections.  Near impossible conditions (once again), low light under a tree canopy, distorted subjects darting about but I took few pics of this intriguing mass wildlife event.  Funny thing though.  I spent over an hour at this spot on a well used footpath trying to get some passable shots and waiting for a bit more light.  In that time, only one other person noticed what was going on and paused to watch it.  We had an interesting chat speculating about the phenomenon.  

So far, I haven’t been able to work out what species these fish are.  Best guess (not particularly well informed on my part) is going towards young chub or dace and there is an odd small perch to be spotted in one photo.  I’d be interested if you know.  

Nikon D500 with Nikon 70-200mm f/4 lens and polarising filter (essential).  ISO800-1600 at f/4 and 1/40-1/160s shutter.  I very rarely use a polarising filter.  Really the only time it does get used is to remove reflections and, as here, that normally means reflections on water.  The first photo in the sequence is one taken on a later visit and for this I used an off camera flash to give a smaller aperture (more depth of field) and better illumination of the fish.  It turned out to be a tricky task to get the flash to penetrate the water rather than to simply bounce off the surface.