He describes the "Thames", naturally free flowing, to have become "chartered" connoting restriction. He is scathing of the sheer control the authorities have, it even seeping down into nature - the oppression is so powerful that even nature is not exempt from its detrimental imapct. - This links back to tropes of Romantic poetry, centralising their poetry around nature. Blacm inverst this and makes it current with the bleak setting he is in, reinforcing how the awe-inspiring sublimity of nature is being tainted through political corruptness