Referrer Spam Question

I keep seeing some kind of spam showing up in the logs that I’m really not familiar with and hoping someone can explain what it is and what to do about it?

In my logs the referrer shows up as something like:

https://www.mysite.com/wp-admin/SPAMSITE.COM

The destination shows up as any of the various pages on my site.

I’ll see hundreds of these at once sometimes, then it will stop for a couple of days. It looks like it’s really affecting my Google rankings too.

Any idea what it is or what to do about it?