How to kill moss on the wall of an old pond so we can paint?

[lexcat]

We have a large pond that was drained when dd was small she is now 7 and desperate to have her own fish. She has made a really good job getting all the junk out of the pond.
But was a nice turquouise colour on the inside walls and about 1/2 of the old paint is still there the rest is moss.
Is their something I can paint on to the moss to kill it or will I have to spray the moss (not so keen on the spray as it is within a confided space).

Fill the pond up with bleachy water for now and it should go. Then though you will need to make sure the bleach is thoroughly gone ... you dont want to poison the fish. Vinegar works as well.
I think I would hire a pressure washer and blast the moss that way.

bleach is a good idea for a small pond but this is a very large pond. As my friend put it when my dd was clearing it out, "so is that to be your swimming pool"
It's about 4m long 2m wide with a depth just over a metre.
Was going to pressure wash, not sure how good sufaces of the wall are. At the same time aware I way have to do that to clean the walls before painting.