Are the swans pinioned or clipped (unable to fly)? Could they have walked to the lake or were they chased or picked-up by someone?

Is there a way to close down their exit from the lake, i.e., fencing, bushes, etc.?

There could be any number of reasons why the swans left your lake. Are there a lot of people, dogs, cats or other natural predators around your lake?

Is your lake drying from a drought? This may significantly reduce aquatic vegetation which might be the reason the swans left your lake.

If they were our swans, we would try to round them up and bring them back to the original lake. This will allow you to keep an eye on them. If no one else will take care of them, the chance of the birds' survival alone will be significantly compromised.

Try to use a couple of kayaks and herd the swans to an area that you can easily corner and capture them. Let us know the outcome. The Regal Swan