Pond footings help

If I want to build a collar like below Do I need to put down some footings or can I build straight on the soil?

 

The ground will be built up around it after like below

 

Personally I'd say you need atleast four inches of concrete, possibly more under the dwarf wall.
Tend to think if it was me I'd add some reinforcing bar as well.

 

I'd put footings down if only to give you a flat level to lay the brick from, if it's on soil, in soil it'll move around a lot and crack and break up with varying moisture levels in the soil around it.
just think when you leave a large pot to go bone dry, the soil shrinks so much it peels away from the edge and leaves a gap.
same for the pond, the outside soil shrinks and is no longer holding the wall plus the pond waters weight up, the wall will tend to bow out opening up the mortar.
with footings it'll have more chance of staying put and in one piece

 

hi, i imagine that you have already got started on this but i did something very similar with my pond. Yes i would (and did) put footings down, as suggested 4 inches should be enough. Also, i did a twin wall, so an inside layer of bricks as well just to make sure. I then filled it with cement to the top layer of breeze blocks, topped it off with house bricks, filled with soil and sowed grass.