If the fish are increasing, it can't be bad!

You can top up with tap water, although fish don't seem to like highly chlorinated water.

You could also get a UV filter and pump.

Hi Longdogs. Is your pond water level going down in this weather?

I used to have a koi pond which I constructed myself, dug the footings and built a raised pond out of brick, it had an unusual shape as I built it like a slice of cake ( shape wise you understand) , sadly I lost all my beautiful koi during the harsh winter of 2010/11, although my son filmed them and they're still on you tube somewhere
BTW LD, your pond looks lovely

With that in mind, any advice on how to protect my pond in winter? No doubt York may get colder than Manchester, but we have our moments

First is a picture of our pond a few years ago. The reeds at the back have now grown enormously, no doubt benefiting from the fishes' 'additions' to the water!

The second shows our goldfish, again a few years ago. Not as many now. I counted 18 (but sometimes 17 and sometimes 19 - the buggers won't sit still!), but bigger. You might also make out a frog basking on one of the lily pads.

The third shows a pond lily. They haven't flowered yet this year, but plenty of leaves so far.

We, too, have a filter with UV, and would recommend one to anyone installing a fish pond. They can be expensive, but certainly keep the pond clear and clean. Having said that, our pond water does become slightly green on bright, sunny days, and I have taken to erecting a large umbrella adjacent to the pond in order to keep the sun off. It seems to help.

I have a pump,that was here. Topping up from the tap??-I do a little bit of that but I`m on a meter. I need rain.

The original pond was/is just too shallow. I dug out a pond when I moved to this area in 1993. It was hard work and did not come free in a Lucky bag,but it was 3ft deep in places with all the shallows for wildlife.

If your pond is three feet deep, they should be ok but it's the ice on the surface that kills them - it traps the gases in the water and sometimes they can get frozen in the ice. I had that happen once where a fish had been stuck all day but after thawing with a hair dryer it was fine. I would suggest a pond heater in the winter or at least a tennis ball which floats around and prevents complete freezing.

That's an incidental advantage of having a fountain. Even when the pond freezes and is covered in snow, there is still an area free of ice where the water enters and, of course, the pond water is still being aerated.

Great pictures JBR. I think that bird is wondering where the water is coming from.