We definitely saw it. I put some blue masking tape on the concrete post that our slip finger rides up and down and in about 25-30 minutes we'd dropped 4-5 feet, then we rose back up again (the tape now under water so I don't know how high). We kept rising and falling for quite a bit and the marina is lucky that it didn't strike at low tide or the gangways could have ended up damaged.
Mother nature is pretty awesome.
-Sven