Water beetle.

Water beetle.

Observation - Water beetle. - UK and Ireland. Description: An aquatic beetle which looks something like a great diving beetle in colouration, but in miniature form. The abdominal portion of what appears to be a dead great diving beetle, which was found at the same upland lake that day is present to give an idea

An aquatic beetle which looks something like a great diving beetle in colouration, but in miniature form.
The abdominal portion of what appears to be a dead great diving beetle, which was found at the same upland lake that day is present to give an idea of proportion.
I think the smaller beetle is approx 8/9mm, though I am guessing using the larger object as a guide, Great diving beetle being up to 35mm in size. The nearest likeness I have found so far is Colymbetes fuscus, but it seems to have fine striations on the elytra where as mine is smooth. Any help greatly appreciated.