why is all this swap space being used?

I have a Debian box, where I am doing some data recovery using ddrescue on a sata ssd. The process has been running for 24 hours, and has 24 to go (at least) in any event, the PC has 16GB ram, and 10GB swap. For some reason, There is 8GB swap in use, and 2GB RAM in use. This seems like an inefficient use of resources. I'd like to avoid this behavior in the future. Why is the memory devices being utilized in this way? And what can be done to avoid this sort of operation in the future?