Is This Purple Loosestrife

It looks very much like it. Lythrum salicaria.

Yes. Let it grow and seed around. They are every bit as good as many cultivated garden flowers.

~yes and mine is coming back from the dead Dawn~I can send you some next week?

Thanks all, that's good news. I've no idea where it has come from, never had it before.
Arlene: Thanks very much for the offer but I've grown some from seed this spring. They are about 6 inches high now and I've set them all the way around the pond - but this isnt one of them. Thanks again everyone.