I peeled back some of the vegetation today. The brown soup at the bottom swirled a lot, and then kept on moving, so I'm assuming there are lots of frogs and newts down there. One frog stuck his head out to check me out.
Even if I roll up the vegetation to remove and reduce it (leaving it on the side for critters to get out), I'm not sure how I'm going to empty the brown soup and inhabitants into a new pond. The vegetation is around 6 inches at the clearer end. The other end is very congested - I used a saw to cut through it before.
We have a very small pond (moulded liner) with two fish (inherited from the previous house owners) and a few plants in it. I tend to clear it out in March, before anything starts growing, using water butt water and a large bucket of original water. I have no idea if this is the right thing to do, but the fish seem happy and the plants grow!
The brown soup will be packed with invertebrates of every kind. Frogs hibernate/ shelter in the bottom of ponds, and as we might yet have freezing temperatures, it would not be doing them a kindness to chuck them out.
The vegetation does need clearing/reducing, and it's best to do that now before breeding season starts again. But there really isn't any need to clear out a pond otherwise - in fact you do much more harm than good if what you want is a wildlife pond (different considerations apply to a fish pond).
However, you say that you think it needs to be re-lined. Then there is nothing for it but to scoop out the sludge complete with inhabitants, put it into containers, and replace it afterwards. This is probably the best time to do it.
As pp said, when you top it up, use rainwater. If you don't have a water butt, get some big tubs of tap water, put a bucket or rainwater in each one, and let it stand in the open air for a week or so.
@traviata I think you're right. I've dip sticked the brown sludge and it's a foot deep. By 4 foot by 8 foot approx. I'm going to have to find a lot of buckets, buy a paddling pool or dig a new pond somewhere else and then move everything over.
Best not to leave it too long if you are going to do it, that frogspawn appears surprisingly early. I get caught out many years when I should have cleared the plants out but haven't got round to it before the frogs & newts get amorous.
@traviata I left it too late last year as the frogs get active surprisingly early. I'd even bought the arm long gloves in advance over Christmas so I could crack on with it, but forget of course. But the liner leak was so bad last year we were having to top the pond up with the hose pipe every week so there was water over the soup.