See posts 4133 and 4134 on Essex Birding thread for info on parking, etc. My post should have said 'far-western end' rather than just 'far end'. (Usually, people explore Heybridge Basin by starting at the other end - parking in the free car park at Heybridge Basin, which I think is called Daisy Meadow, or something like that.) The Great Grey Shrike make shift locatation, but it has been at the far-western end in recent days. I believe that the Short-eared Owl is usually to be found in the eastern-to-middle section, by the sea wall. Don't forget to look out of the Bearded Tits in the reeds. Good luck.