Mystery swimmer in the wildlife pond

[Sheepherd]

We have a pond inthe field which has been populated entirely by wildlife without any human intevention.
A new sighting to day was of a slug size and shape swimming along without any visible legs, pretty sure its not a newt we have alot of them, Could it be a flatworm of sorts. It swims by weaving its body, quite elegantly really.
Any suggestions would be appreciated. I will try and get a photo but it's only appeared once.
The pond is in thick clay and fed from a ditch when there is enough water for it to run. The level does not vary by more than an inch. Depth varies from 5-6' down to gently sloping sides as well as some steep sides.
regards

[roobarb]

An unusually brazen leech?

[The Woodman]

I'd say that was a pretty good description of a swimming leech, Sheepherd. They swim with a continual wavy motion, up and down rather than side to side.

There are many species, one of the larger common species is the Horse Leech.

By the way, welcome to WAB.

[Sheepherd]

Thanks to you both for your response. Its a good job the grandchildren are now too old to swim in the pond. My only reservation is that the body was or appeared to be of equal thickness for the whole length and it was "b****y" big.