What is it?

It's a mimulus ("monkey flower"). Someone else will probably give you more details.

I agree with Readejahn

Yep i concur!! they like it damp, often grown near to ponds

They also self seed as I am finding out. I have a couple popping up in the garden right now and I'm sure I didn't put them there! Yippee, free plants.

thank you very much to all for identifying the above, we have a pond so that where it will go