On Walthamstow marshes where they seem to have been cutting the long grass and baling it up. Hard to believe the Olympics were 10 years ago. I had the best time, it's not often the Games come to your home town.
If you're maintaining hay meadows for that ecology, you do need to mow and remove grass when the seed heads have had a chance to set, which is usually July and to my with-a-little-bit-of-knowledge eye it looked about right as things look early this year. The same has happened locally on those places being maintained environmentally (although a few were mowed far too early).
@phil_howcroft the main venue was just south of here at Stratford. And one of the other venues, can't remember which now, was in the borough. And if you follow this path for 3 miles or so, you'll be in the Queen Elizabeth Olympic Park, one of my fave cycle routes along the Lea.