We go in and out of classrooms all day, every day, and along the way have watched the Thames' noticable tides. We're just a couple days past the New Moon, meaning it's spring tide. Today the BBC weather centre predicted a 7-meter (22-foot) spread at London Bridge, just upriver from our hotel.
Here's low tide, around 10 this morning, from the hotel:
Now high tide, about 4 this afternoon:
Here are side-by-side comparisons of Butler's Wharf:
This happens because this far downriver the Thames is actually an estuary all the way to Teddington Lock, well past London.
One notices these things when one has a break in a 4-hour financial accounting class.