Pond emergency

Hello people
I inherited a pond when moving house it has one or two koi carp in it. I gave the pump /filter a clean out and lost the sump plug very stupid of me. Thought I had fixed it up DIY style but later in the day found it had breached and most of the pond water has escaped to my garden Leaving me a muddy pool . Emergency measures I had to give the pond some tap water is guessing between 1/3 upto a half tap water now about 20cm deep
I have seen one fish once
but they are always very elusive. I also left some tap water to sit and 'dechlorinate' over night to top up Futher.
Question is will this be ok to top up with now or is it nessecery to use a tap water purifier? And where might I find this stocks are low or take a few days to arrive right now.
Will upload a few pics in abit
Any help at all welcome

 

Here's a few pics iv measured it at 17cm deep with 2_3 cm of fine mud/silt at the bottom. This mud does bother me at usuall times is it something I should be removing or is it a good habitat for Mr fish?

 

Thank you very much for your advice. The missing 'sump plug' is from the water pump. I jammed it with a lid a plastic glove and a big stone looked quite safe obviously not good enough. It came loose it sucked the water out and deposited in the garden. I noticed just in time for the poor fish but too late as well.
The pond is water tight in itself just lacking water.
I have found places online to purchase but they are not currently delivering.
I'm sure Mr fish would appreciate a bit more water at the moment so I'm topping up with buckets after allowing to sit for a while.
I love the Lilly's when they come out and will try to camaflage the whole side of the pond future any suggestions on good plants for this are great.
Thanks again for your thoughts and ideas

 

I take it was a plug in the filter box??

I've had a few mishaps myself over the years, mostly with the filter getting blocked and overflowing.

For that reason I dont have the pump on the bottom, that way it can never empty the pond entirely if something goes wrong.

 

Some good advice from Mr Pond - ARMANDII .

There are arguments for and against both preformed and liner ponds. It comes down to personal choice I think.

I have a small preformed pond and it does the job that it is intended for very well, which is provide a home for wildlife. However as ARMANDII has said they are not as easy to blend into the surrounding area. As well as growing grass and flowers right up to the edges there are other things that can be used to soften the pond edges. I have some pieces of slate ( former roof tiles that were dumped on the beach ) which I've overlapped along one edge. Also made a log pile on one side and brought the wood right up to the pond edge. I've planted a hardy Geranium in the wood pile so it spills out across the wood. I don't know what your garden looks like @Ruth82 but if you post pics of it we can all think of creative edging for your pond

 

This is an excellent tip I didn't think about will definitely be doing in the future thank you