Stick with it, eventually they descend into the reeds.
Just a snippet of an entry, a video of the Starling roost at one of my local patches, Kings Mill Reservoir. Perhaps only 250 birds and yet still a display worth getting away from the TV to go watch. Amazing how they all coordinate to form such dynamic flocks. There's some insight from a study (here) in Rome that goes some way to explaining the phenomenon. Lots of techno-babble in there, but the gist seems to be that each individual bird orientates itself against only the handful of other birds around it. Multiply that by a thousand or a million and hey presto, one of the more remarkable behaviours to be found anywhere in the natural world.
Speaking of Starling roosts, I'm at Carsington at the weekend, not only will it be an Aren't Birds Brilliant event, we have Feed The Birds Day too(!). At the end of the day in the autumn/winter months there's a significant roost in a nearby village called Kirk Ireton, of upto 100,000 birds. No news on it yet this year, so perhaps I'll go have a look for myself.