It seems to work.

A year or two ago, we learnt that barley straw was very useful in clearing up green water in ponds without the requisite % coverage of leaves.
We tried it - it worked. 
This year, perhaps understandably, my mind has been "elsewhere".
I had a feeling "we" tended to buy things in twos and had no idea where the other was. 
Fortunate coincidence ... I'm building some "Lasagne" raised beds and, consequently, had some barley straw to hand.
On a recent Thursday Bro-bond Jerra and I remarked that the pond was a bit less green, though still noticeably green.
This Thursday ... behold. 
You are gazing down through about 18" (50 cm) of once-green pond water.