Sounds   
You can find a sound map (which includes lea marshes) on the rather excellent London Sound Survey web site at http://www.soundsurvey.org.uk/index.php/
A video mainly about the mist coming off the Lea, also features the Dawn Chorus plus the sound of trains rattling across the marshes on a summer morning. Click the link to see and hear it.Lea Haar June 2013
Lea Marshes   Videos