Little pond

Perhaps you could shade it a bit with one of those miniature waterlilies or some frogbit? But you could perhaps site it to the north of a clump of taller planting or perhaps a big rock so the water wouldn't get as overheated? Or add one of those little solar waterfalls to help aerate it? Anyway if it didn't work you'd have a nice half barrel for planting something else in...
Tiny ponds can be difficult to balance but if you've done it once...

Hmm.

There's nothing to lose really - give it a try!

I have a wooden water feature facing south I have Iris water lilies that do well in it. Its not as deep as a real half wooden barrel.

How's it been coping in the hot sun we've had Thrupennybit?

It's coped well my water Iris also the small water Lily s has flowered they are all doing very well even with the water level going down with evaporation about the same as yours. It is exposed to full midday and afternoon sun no shade.

We have a wooden half barrel pond in a very sunny spot in our garden, with a large water lily, we top it up most days, mainly because it is leaking!!.....we have planted around it....( one half) for the 3 frogs, they need the cover, especially in this heat.,..will post a picture or two!

The frogs also need access in and out.

It is sunk into the ground.....