Skarol98, I am not sure if the new pond is your first pond, or you have had previous pond experience, but I will try to give some ideas as to why your plants did not survive.
Insects and animals can destroy plants. If it was animal related, you would see evidence. If it was insects, you might not notice until it was too late. Aphids, roller caterpillers and spider mites are quite often the insects that destroy pond plants, although there are many others.
A mistake new ponders make sometime is that they want their pond to have crystal clear water and add a lot of chemicals and filtration to achieve that goal. Plants can survive in clear water, but they have some needs that must be met.
Hyacinth are floating plants whose roots filter the water. They get their nutrients from the water as they do this. If the water is filtered too strongly by other means, they starve to death.
Water lilies must be planted in soil that will hold their roots in place and allow them to be "anchored." They need to draw the fertilizer out of the soil, so they need to be fertilized as needed on a regular basis also.
Both types of plants need warmth and sunshine also. Lilies and hyacinth will not do well in total shade, even if the water and air is warm enough.
I ma not sure if this helps you or not, but maybe it will help someone who is starting out with their first pond.
