[The Mouth of Sauron]

As they were leaving Lorien Celeborn spoke to the Company - and it was obvious he was well informed about events in Middle-Earth. For example, he knew about the bridges at Osgiliath being down and the eastern bank of Anduin being held by the Enemy. He must have got his info somehow.

And as the Company was approaching Rauros Aragorn did state that boats in recent times had travelled down Anduin from Wilderland to Osgiliath - Boromir confirmed this, although he said it had happened "seldom". Might these boats have carried Elves from Lorien and also possibly from the Woodland Realm in Mirkwood ? Anborn knew about black squirrels in Mirkwood.

Another possibility I suppose would be Gondorian ships sometimes going to the Gulf of Lune, and/or Cirdan's mariners visiting Pelargir.