The Nandor-Lenwe's people?
 

I know that Lenwe led his people down Anduin and that some of them stayed age-long in the woods of the Vale of the Great River, and some dwelled at the mouths near the sea, and some between Ered Luin and the Misty Mountains, but then I get confused... Is it possible that this could be the reason why the people of Dol Amroth are said to have elvish blood, or is that just due to Mithrellas who accompanied Nimrodel, or even just because Amroth was lost in the near vicinity?

Silly question, I know, but these things do confuse me so...

The small elvish haven was said to be an improtend fact in the history of Dor-en-Ernil, but there is no record of any mixing blood with the elves other then Mithrelas and Imrazor.

Thus the people of Dol-Amroth who had elvish blood were only the members of the Line of Dol-Amroth following Imrazor.

Respectfully
Findegil