Invasion of tiny green fish?

and still ricky villa

I know nothing about fish unless they're in breadcrumbs so excuse my ignorance...

I went for a swim in the sea earlier and after a bit of a warm up came back to land and there were loads of little silver fish about 2-3 inches in length along the shore. They were washed up alive and I noticed a dog walker looking at them. She said she'd never seen anything like it in 30 years walking that beach. We walked down the beach for a good bit and more and more fish were being washed up.
She went off and I thought I'd continue my swim but only got a few metres out when I had to come back in cos there were thousands of little green fish about an inch long in the water.
I kept walking up the beach to try to find a clear spot but it was impossible to find a spot that wasn't swarming with these little green feckers

Now I know they would have done me no harm and it's hardly the apocalypse but does anyone have any ideas what it was all about?

Unpossible

Sounds like sprat. A huge shoal of them hit Tralee bay two years ago, they were everywhere, loads were washed onto the beaches. They were followed by mackerel.