Black, furry and fast!

Something caught my eye (well, just the corner of it) it was black, furry and fast. That was a few days ago, and I have already done some research via google to try to ascertain what it was. This morning, in a different area I saw another BFF, and am wondering if it is possibly a water shrew?
There is a pond in the back garden, and a very overgrown wild area with a ''water hole'' out on the site...would this be a suitable habitat for this shrew?
There are several areas with holes in the grass which are not moles, and so I have assumed this to be voles, now am wondering if it is in fact shrews.
Can anyone share some knowledge or experience please ?

 

How large is it?

 

@longk - the BFFs are about 7 - 10 cm in my estimation, although they are like quicksilver, and there was no time to even say tape measure.

Woo.... there is a camping rally here this weekend, and some suspicious characters out there
I have heard laughter, and am wondering if I should remind them that`s not really allowed.... tut! What do they think this is - a holiday camp ......thank you for the description, I shall go spy on them and see if one is wearing a ''super'' cape.

It will be interesting to find out if there IS a colony of water shrews out there.

 

Rules out Mink then. It doesn't rule out young black rats if you're near the coast though.

 

I think Mink are a lot bigger, and I have seen them in a nearby park. They don`t move like rats - I would definitely have recognised those ! These little creatures move like quicksilver!