It's pickerel weed, I've got a few in my pond. There's a white variety aswell.

I understood that this is known as Arrowhead, got one in my popuppond and it has the same flower.

I think it's pickerel weed as well. The arrowhead leaves are more pointed than the pickerel weed. I have both in my pond but the arrowhead is new so I havn't seen it flower yet.
Alison

ItÂs defiantly a Pickerel, I have one which has been flowering constantly since July.
Arrowhead has a slightly different shaped leaf and totally different flower. If you want to see pictures of the two have a look on bromfieldaquatics as they have pictures of both.

Here is a link that might be useful: Broomfield Aquatics

the flower on my plant isn't a 'spike' it's a small neat halo with a small pointy middle, about 1cm in total. I'm not sure it is Pickeral as that seems to be a longish spike of flower head. I'll get the camera out again and take photo from a different angle.

I still think it is a Pickerel, it just has a short 'spike'. If you just take the top of the flower in the small picture I suspect that's pretty much what you have. Next year you will get the full size flower spike(s). The first year mine was in I only got a couple of tiny flowers.

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Yes thats it, top picture flower and the leaves are identical. I really don't know where mine came from. It must have been a tiny seedling on some other plant that I bought. cheers folks