Diving Beetle.

 Biots, rubber legs and fine black flash for the legs.

 A silver glass bead for added flash.

Thin skin and raffia make the shell.

 The "Old Man's" new favourite fly.

I'm sure Toad knew all about them.

A friendly man on a pond suggested using a Water Beetle. You gotta love those old boys! This is what I came up with and .... well take a look.