what is it?

what is it?

Observation - what is it? - UK and Ireland. Description: I rescued this bug from our pond, the sun was bright when I took the photo so does not show colour well. it was a bright green, except for the triangle at the bottom which was a reddy colour.

I rescued this bug from our pond, the sun was bright when I took the photo so does not show colour well. it was a bright green, except for the triangle at the bottom which was a reddy colour.