River foam

The high water at the weekend  has resulted in foam being produced on the river along the Ock valley walk:

I've noticed this before on the Ock and other rivers and thought this blog would be an opportunity to try and research it.  The foam seems to be made by surfactants - 'a substance that reduces surface tension' (Oxford English Dictionary).  The resulting reduction in surface tension and the faster flowing water creates bubbles which are moved by the wind and the currents to the calm parts of the river where they accumulate - resulting in the foam, in this case forming by one of the weirs.

There appear to be two possible causes of these surfactants,  natural organic material - decomposing plants and animals, the rate of this could be caused up by an increase in temperature or pollution or man made material - detergents for example.
As there is not a lot of it  and there has been a sudden increase in temperature and water flow, coupled with the lack of industry along the river (especially any which are likely to produce detergents) it is probable this foam is natural - although it doesn't look like it.  I hope to go back at the weekend to see if it had dispersed. 

This article proves a remarkable amount of foam can occur naturally (if a man-made dam is considered natural) without any pollution: http://www.dundeeonline.com/articles/12.1.2003.html

As always, if anyone knows anything more about this, I'd be very interested to hear.

References:
http://www.in.gov/idem/wqsurvey_025surfacefoam.pdf
http://www.duluthstreams.org/understanding/foam.html