I tend to put lilies in a square pond basket that is about 9-12" square. I tie the rhizomes of the lilies into the basket using fishing line and then fill it with gravel. I don't use aquatic compost as in a few months there is enough biological material to provide nutrients for the plants. Over time roots will come out of the baskets into the sludge at the bottom of the pond.
I have fish in the pond so they rummage in the bottom looking for food.

I meant to ask is your pond concrete lined or with a liner.

at this time of year the lily will be in full growth. try and put it at the same depth as it was ie the leaves floating on the surface. it wont matter if they are a little deeper say and inch or 2 as they will elongate their stems. if you have a fountain or waterfall in it then place the lilies away from it, they do better in the more still water.

if there are shelves arounfd the edge then they are for putting plants that are called marginals. yellow flag iris , reeds, rushes, water mint bog bean are examples. lilies water hawthorn are true aquatic plants and root in the bottom of the pond.

Not all lilies enjoy the same depth of water so it would be good to ask the person who gave them to you how deep they were planted before. At this time of year whatever the final depth of growth is going to be the leaves should be allowed to float, so if they if the stems are still too short put the basket(s) on some kind of support to bring it near the surface until the plant has grown some more.
You will also need plenty of oxygenating pondweed for a pond that size to prevent the water turning green..

Thank you. The pond has an EPDM liner which seems to be holding the water ok. No leaks yet! I got the lilies from my daughter who does not know the name of them but said they are native ones and a large size. I will have to wait and see. They are in a bucket at the moment but I will get them into the pond ASAP. The pond went green recently so I purchased some plants off ebay - Veronica Beccabunga, Lysimacia Numularia, Crocosmia and Dwarf Bullrush. Two are looking good, one looks sad and the other has gone to plant heaven. The pond is now clearing to a brown colour and looks like a large cup of tea without any milk in.There is a shelf running around the pond but it varies greatly in depth from about 6 inches to about two foot. I will have to read up on which plants to buy for each depth. I also got some duck weed which seems to be quite happy floating about. Thank you again for you help and good advice. Cecelia

Hi Cecelia, that's not a pond, that's a small swimming pool, !!! 😊😊😊. Derek.

are the lilies yellow flowered That is our native one Nuphar lutea. There is a European one Nymphea alba which is white.

personally I'd get the duck weed out before it covers the whole surface of the pond. it becomes a real nuisance. There are some good sites on internet about pond plants. The Rhs is a good source of info.
https://www.rhs.org.uk/advice/profile?pid=448

I agree, I spent ages yesterday trying to decrease the amount of duckweed. No matter how much you remove it will be back... When I said you need pondweed I meant the kinds that are submerged all the time. With enough of that your water should remain clear. It also grows rapidly but is easy to pull out if there is too much. Its a good refuge for all kinds of pondlife - tadpoles, water boatmen etc etc..

Thank you Seaburngirl. I think it is the white one but will have to wait and see. My daughter's duck eats everything it can and goes mad if you go near the pond. She just quickly pushed her entire arm into the pond and gave me what she managed to grab before the duck chased her away. Duck rules OK

My pond is covered in a thick layer of duckweed at the moment but removing it means death for a lot of late-stage tadpoles which get caught up in it as I simply can't rescue them all, so I'm relying on the pond plants, a solar powered aerator and a hulahoop. The hulahoop keeps an area of the surface clear for a few days at a time and then I have to clear an area of water and reposition it.
Apart from online advice. the RHS has issued a helpful book in its Practical Guides series, entitled 'Ponds and Water Features'.

Great Idea I will get a copy thank you