Try to wait for the swans to take a break which should occur at the first of the nesting process. Once nesting gets really serious, the swans may not leave the area. In this case, you will be confronted by a very defensive parent protecting its eggs and young. Clean around the nest being careful not to disturb any nesting material especially around the bowl. Once the parents spot you, you will have approximately 2-3 minutes to get in, do your thing and quickly leave. If the swans see you they will always be defensive around you if they see you again. So, if you can be sneaky and quiet, you may be able to do this without being noticed. Just don't wait in an open area that they can sense you are waiting for them to leave because they won't. Good luck. Let us know how this works out. The Regal Swan